Chemistry grade 7

Mass is a measure of the amount of

matter in an object. It is a measure of the amount of material that makes up an object, and it
is usually measured in grams or kilograms.

Matter exists in three physical states

(1) Gas
(2) Liquid
(3) Solid

(1)Gas - Has no definite shape but it fill the container

(2) Liquid- Has no fixed shape but assumes or takes the shape of its container
(3) Solid- Has a definite shape and volume.

Properties of Matter
There are two properties of matter.
(1) Physical Properties.
(2) Chemical Properties

Physical properties
The physical properties are
(1) Density
(2) color
(3) Physical State
(4) Melting Point
(5) Hardness

Chemical properties
The chemical properties are:
(1) Mass
(2) Length
(3) Temperature

Types of change

We have two types of change

1. Physical change
2. Chemical change

Physical change
A physical change is one which is easily reversed and produces no new substances
For instance:-
The dissolution of common salt in water is a physical change because no new substance is
formed and the salt can be recovered by evaporating the salt solution to dryness.

DIAGRAM SPACE

Another Example is Melting of ice, when ice (solid water) melts, it becomes a liquid (water).
The chemical formula for water is still H2O before and after the change. This means that the
water molecules haven’t change, but their physical arrangement has changed from solid to
liquid

Chemical change
Chemical change is the transformation in which a new substance is formed and is not easily
reversed

Example:-
Burning of wood is a chemical change because you can not reverse it back after burning

DIAGRAM SPACE

Another example is rusting of iron, when iron rust it reacts with oxygen in the air to form a
new substance called iron oxide

Class work
1. What is a mass?
2. Define matter.
3. A mass is measured in ____________
4. Matter exist in how many physical states? Name them.
5. Which of the matter physical states has no definite shape?
6. Which of the matter physical states takes the shape of it container?
7. How many properties of matter do we have? Name them.
8. What is chemical properties of matter?
9. Explain density.
10. State the types of change and which one is reversible

Hardness:- refers to how resistant a substance is to being deformed. Imagine we have two
different metals, one is a soft metal like a copper and the other is a hard metal like a
diamond. If you try to scratch copper with a knife, it will easily get scratched but if you try to
scratch diamond with the same knife, it won’t get scratched easily. This means diamond is
harder than copper.

Chemical properties

Chemical properties of matter are the characteristics that describe how a substance
interacts with other substances or changes into different substances

Examples are the rusting of Iron

Mix

Salt + water

Assignment

Define the following and give two examples each

(1)Pure
(2) impure substances

Pure and Impure substances

Pure substances:- These are materials that are made up of only one type of particle
This means that they have a unique and definite composition

Examples of pure substances:

1. Pure water: Water that has no impurities or other substances dissolved in it.
2. Table salt: it’s a Sodium chloride that is pure and has no other substances mixed in it.
3. Gold: it’s a precious metal that is pure and has no other substances mixed in it.
4. Oxygen: it’s a gas that is pure and is used in hospitals to help people breathe.

Impure substances:- an impure substance is a material that is made up of two or more

different types of particles. This means that it does not have a uniform and definite
composition.
Examples of impure substances:

1. Seawater: Water that has salt and other substances dissolved in it.
2. Air: The mixture of gases that we breathe, which includes nitrogen, oxygen, and carbon
dioxide.
3. Salad dressing: A mixture of oil, vinegar, and other ingredients that are not uniformly
mixed.
4. Sand: A mixture of different minerals and particles that are not uniformly mixed.

Way to separate the components of an impure substance

Filtration:- Filtration is a way of passing the mixture through a filter paper or a porous barrier
that allows only certain particles to pass through.
For example, if we have a mixture of sand and salt dissolved in water, we can filter the
mixture to separate the sand particles from the salt solution. The sand particles will be
trapped on the filter paper, while the salt solution will pass through.

Evaporation:- Evaporation works by heating the mixture until the liquid component
evaporates, leaving behind the solid component. For example, if we have a mixture of salt
and water, we can evaporate the water to separate it
from the salt.

In summary,

Pure substances are like a single flavor of ice cream, while impure substances are like a mix
of different flavors. Pure substances have a consistent and predictable composition, while
impure substances have a more variable composition and may exhibit a range of properties.

Classwork
1. Give five types each of both pure and impure substance apart from the ones in your
note
2. Explain filtration according to your understanding
3. Explain Evaporation according to your understanding
4. _________ are materials that are made up of only one type of particle
5. _________ have a uniform and definite composition
 6. __________ are material that is made up of two or more different types of particles
7. What holds solid in filtration?
8. Explain what you understand in the process of evaporation

Assignment
1. Define an Atom
2. State the component of atom

Atom, Element and compound

Atoms are the fundamental building blocks of all matter in the universe. They are the
smallest particles of an element that still retain the properties of that element. Think of
atoms like LEGO blocks - they are the individual pieces that can be combined in different
ways to create something new.

Atom is made up of three subatomic particles:

(1)protons (2)neutrons (3)electrons.

Protons:- have a positive charge

Neutrons:- have no charge

Electrons:- have a negative charge.

The number of protons in an atom determines the identity of the element. For example,
all atoms with one proton are hydrogen atoms, while all atoms with six protons are
carbon atoms.

Elements
Elements are a type of atom that has the same number of protons in its nucleus. They are
organized on the Periodic table, which is a chart that organizes all the elements in order of
their atomic number.

The periodic table is a useful tool for scientists because it allows them to quickly identify the
properties of an element based on its position on the table.

Show her a Periodic Table

When elements combine with each other, they undergo a chemical reaction that creates a
new substance called a compound. A compound is a substance that is made up of two or
more different elements that are chemically bonded together.

The resulting compound has its own unique properties that are different from the properties
of the individual elements that make it up.

For example
When hydrogen and oxygen combine, they form water - a compound with properties that are
different from both hydrogen and oxygen. Water is a compound because it is made up of two
different elements (hydrogen and oxygen) that are chemically bonded together.

In summary, atoms are the building blocks of matter, elements are a type of atom with the
same number of protons, and compounds are substances made up of two or more different
elements that are chemically bonded together. Understanding the relationships between
atoms, elements, and compounds is fundamental to the study of chemistry and helps us
understand the behavior of all matter in the universe.

Classwork

1. What is an atom?
2. State the subatomic particles.
3. ________ has a negative charge in atom subatomic particles
4. ________ has a positive charge in atom subatomic particles
5. The number of protons in an atom determines the identity of the ________
6. Define Element
7. Explain briefly how you understand the relationship between atom, Element and
compound

ACIDS AND BASES

Acids and bases are two important concepts in chemistry that describe how substances
interact with each other.
ACIDS AND BASES

Acids are substances that taste sour and can be found in foods like lemons and vinegar.
When you put an acid in water, it releases hydrogen ions (H+), which makes the solution
more acidic. Acids can also react with metals and carbonates, producing bubbles and fizzing.

BASES
Bases are substances that feel slippery and taste bitter. They can be found in things like
baking soda and soap. When a base is mixed with water, it releases hydroxide ions (OH-),
which makes the solution more basic or alkaline.

One way to test if a substance is an acid or a base is to use a pH meter, which measures the
acidity or alkalinity of a solution. Acids have a pH less than 7, while bases have a pH greater
than 7.

In summary, acids and bases are two types of substances that have different properties and
reactions. Understanding their characteristics is important in chemistry and has many
practical applications in our daily lives.

So, let's break it down further:

What are Acids and Bases?

Acids:
Taste and Feel:
Acids taste sour and feel tangy.
Examples:
Common examples include lemon juice, vinegar, and stomach acid.
Chemical Reaction:
When acids dissolve in water, they release hydrogen ions (H+). This is what makes the
solution acidic.

Bases:
Taste and Feel:
Bases feel slippery and taste bitter.
Examples:
Common examples include baking soda, soap, and bleach
Chemical Reaction:
When bases dissolve in water, they release hydroxide ions (OH-). This makes the solution
basic or alkaline.

How to Identify Acids and Bases

(1) pH Scale:
The pH scale measures how acidic or basic a solution is. It ranges from 0 to 14.
Acid
Have a pH less than 7. The lower the pH, the stronger the acid.
Neutral:
Water is neutral with a pH of 7.
Bases:
Have a pH greater than 7. The higher the pH, the stronger the base.

(2) Litmus Papers

This is a special paper that changes color when it comes into contact with an acid or a base.

Blue Litmus Paper

Turns red in an acid and stays blue in a base.
Red Litmus Paper
Turns blue in a base and stays red in an acid.
Purple Litmus Paper
A purple litmus paper turns red if the given solution is acidic and turns blue if the given
solution is basic in nature.

Why Are Acids and Bases Important?

Everyday Uses:
Acids:
Used in food preservation, cleaning, and in the production of chemicals like plastics and
fertilizers.
Bases:
Used in cleaning products, antacids, and in the production of soaps and detergents.

Biological Importance:
Acids:
Our stomachs use hydrochloric acid to help digest food.
Bases:
Our bodies use bicarbonate (a base) to neutralize stomach acid and maintain a healthy pH
balance.
Summary

Acids:
Sour, release H+ ions, pH < 7.
Bases:
Bitter, slippery, release OH- ions, pH > 7.
pH Scale:
Measures acidity or alkalinity from 0 to 14.
Litmus Paper:
Changes color to indicate whether a substance is an acid or a base.

Understanding these concepts helps us know how different substances interact and how
they can be used in everyday life.

Properties of Acids and Bases

1. Properties of Acids
● Acids are corrosive in nature.
● They are good conductors of electricity.
● Their pH values are always less than 7.
● When reacted with metals, these substances produce hydrogen gas.
● Acids are sour in taste.
● Examples: Sulfuric acid [H2SO4], Hydrochloric acid [HCl], Acetic acid [CH3COOH].

2. Properties of Bases
Some properties, like a bitter taste, are owned by all bases. The bases feel slippery, too.
Dream on what slippery soap looks like. And this is a foundation. Furthermore, when
immersed in water, bases conduct electricity because they consist of charged particles in
the solution.
● They are found to have a soapy texture when touched.
● These substances release hydroxide ions (OH– ions) when dissolved in water.
● In their aqueous solutions, bases act as good conductors of electricity.
● The pH values corresponding to bases are always greater than 7.
● Bases are bitter-tasting substances which have the ability to turn red litmus paper
blue.
● Examples: Sodium hydroxide [NaOH], milk of magnesia [Mg(OH)2], calcium hydroxide
[Ca(OH)2].
Classwork
1. What are the materials / equipment use to test if a substance is an acid or base?
2. Define an acid.
3. Define a base.
4. How does an acid taste?
5. How does a base taste?
6. Why Are Acids and Bases Important in Everyday use?
7. What is a litmus paper?
8. Mention two ways we can use identify the presence of an acid or a base in a substance
9. Between acids and bases which one has a lower pH scale?
10. State two difference between Acids and Base.

Assignment
1. Explain briefly a chemical reaction

Chemical reactions are a fundamental concept in chemistry that describe the process of one
or more substances (reactants) being transformed into one or more different substances
(products). To explain this to a grade 7 student, you can use the following analogy:

Chemical reaction
A chemical reaction is a process that occurs when two or more substances are converted
into new substances with different properties:

Imagine you have a bunch of building blocks of different colors, and you want to build a
specific structure. To do this, you need to arrange the blocks in a certain way. Similarly, in a
chemical reaction, the reactants are like the building blocks, and the products are the final
structure that is formed.

During a chemical reaction, the atoms in the reactants are rearranged to form new bonds,
resulting in the formation of the products. This process involves the breaking and forming of
chemical bonds, which releases or absorbs energy.

To make it more relatable, you can use examples such as:

Example of chemical reactions

1. Combustion reaction: When you burn wood or gasoline, the carbon in the wood or gasoline
reacts with oxygen in the air to form carbon dioxide and water vapor. This is an example of a
combustion reaction, where the reactants are wood or gasoline and oxygen, and the
products are carbon dioxide and water vapor.

2. Acid-base reaction: When you mix baking soda (a base) with vinegar (an acid), the
hydrogen ions from the vinegar react with the carbonate ions from the baking soda to form
carbon dioxide gas and water. This is an example of an acid-base reaction, where the
reactants are baking soda and vinegar, and the products are carbon dioxide and water.

Types of chemical reactions

There are several types of chemical reactions, including

(1)synthesis,
(2) decomposition,
(3)single replacement,
(4)double replacement,
(5)combustion.

Each type has its own specific pattern of reactants and products.

More Explanation

Sure, let me explain chemical reactions in more detail:

1. Reactants: In a chemical reaction, the starting substances are called reactants. These are
the materials that undergo a change during the reaction.

2. Products: The new substances formed as a result of the chemical reaction are called
products. These are the materials that are created from the reactants.

3. Chemical bonds: Chemical reactions involve the breaking and forming of chemical bonds
between atoms. A chemical bond is the force that holds atoms together in a molecule.

4. Energy changes: Chemical reactions can release or absorb energy. Exothermic reactions
release energy, usually in the form of heat or light. Endothermic reactions absorb energy
from their surroundings.

Conservation of mass: In a chemical reaction, the total mass of the reactants is equal to the
total mass of the products. This is known as the law of conservation of mass.
A chemical reaction is a process that occurs when two or more substances
are converted into new substances with different properties:

● Explanation
Atoms in the original substances are rearranged to form new substances. The number
of atoms and the amount of mass remain the same, but the new substances have
different properties.

● Examples
○ Water: Hydrogen and oxygen are both gases at room temperature, but when they
bond to form water, they become a liquid.

○ Baking a cake: The ingredients are converted into a cake, which has different
properties than the ingredients.

○ Burning a candle: The wax on the wick combines with oxygen from the air to
create carbon dioxide and water vapor.

Identifying a chemical reaction

Chemical reactions can be identified by physical changes, such as:

○ Color change

○ Gas formation

○ Heat production

○ Change in smell

○ Change in taste
Reactants and products
Reactants are the substances that interact to produce new compounds, and products are the
newly formed compounds. Reactants are written on the left side of the chemical reaction
arrow, and products are written on the right side.

Classwork
1. Define Chemical Reaction
2. What are reactions
3. What are products
4. Define chemical bond
5. State types of chemical reactions
6. Give three examples of chemical reactions
7. Mention ways of identifying a chemical reaction

THE PERIODIC TABLE

The periodic table is a chart that shows all the elements in the universe. It is organized in a
way that helps scientists understand the relationships between different elements.

The elements are arranged in rows called periods and columns called groups. Each element
is represented by a unique symbol, usually one or two letters, and has a specific number of
protons in its nucleus called the atomic number. The elements in the same group have similar
chemical properties because they have the same number of electrons in their outermost
shell.

The periodic table is a powerful tool that helps scientists predict how elements will behave in
chemical reactions and discover new elements.

The periodic table is divided into several blocks, including the

(i)s-block,
(ii)p-block,
(iii)d-block,
(iv)and f-block.
The s-block:-contains the alkali metals and alkaline earth metals, which are the most
reactive metals.
The p-block:-contains the nonmetals, which are the most diverse group of elements.
The d-block:-contains the transition metals, which are metals with variable oxidation states.
The f-block:-contains the inner transition metals, which are the lanthanides and actinides.

The periodic table also has several special regions, including the noble gases, which are the
most stable elements, and the halogens, which are the most reactive nonmetals. The
periodic table also has a special section called the Lanthanides and Actinides, which
contains elements with atomic numbers from 57 to 118.

Atomic number
The number of protons in the nucleus of an atom of an element. Each element has a unique
atomic number.

Groups and periods

The vertical columns of the periodic table are called groups, and the horizontal rows are
called periods.

Elements
Elements are pure substances made up of only one type of atom. For example, hydrogen (H)
and oxygen (O) are elements, but water (H20) is not.

Properties
The periodic table can help you analyze the properties of elements, such as their
(I)atomic radius,
(ii)electronegativity,
(iii)ionization energy.

Overall, the periodic table is a powerful tool that helps scientists understand the
relationships between different elements and predict how they will behave in chemical
reactions. It is an essential tool for anyone studying chemistry or any other science that
involves the study of matter.

Classwork
1. Define the periodic table
2. How are the elements in the periodic table arranged?
3. What symbol does an helium has in the periodic table?
4. Write out the atomic number of the following elements (i) Calcium (ii) Oxygen (iii)
potassium (iv) Silicon (v) hydrogen (vi) boron (vii) magnesium (viii) neon
5. List the blocks of the periodic table.
6. Which of the periodic table block contains the nonmetals, which are the most diverse
group of elements.
7. Which of the periodic table block contains the alkali metals and alkaline earth metals,
 7.
which are the most reactive metals.
8. The vertical columns of the periodic table are called _______, and the horizontal rows
are called ________

Hydrogen

It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the
formula H2, sometimes called dihydrogen, is a nonmetallic, colorless gas under ordinary
conditions. It becomes an alkali metal under extreme pressure. The atomic number of
hydrogen is 1

Helium

is a chemical element; it has symbol He and atomic number 2. It is a colorless, odorless, non-
toxic, inert, monatomic gas and the first in the noble, Under extreme pressure, it transforms
into an alkali metal.

Lithium

is a soft, silvery-white, metal that heads group 1, the alkali metals group, of the periodic table
of the elements. It reacts vigorously with water. It’s has atomic number 3 and is a silver metal
with a high reactivity.

BERYLLIUM
IS A SILVER-GRAY METALLIC ELEMENT THAT OCCURS NATURALLY IN ABOUT 30 MINERALS.
And has atomic number 4

Boron
is a chemical element. It has the symbol B and atomic number 5. In its crystalline form it is a
brittle, dark, lustrous metalloid; in its amorphous form

Carbon
is a chemical element; it has symbol C and atomic number 6. It is nonmetallic, takes several
forms. It's usually a gray or black solid, although diamonds may be colorless.

Nitrogen (N),
nonmetallic element of Group 15 [Va] of the periodic table. It is a colourless, odourless,
tasteless gas
Oxygen
is a chemical element with the symbol O and atomic number 8. It is a member of the
chalcogen group in the periodic table, a highly reactive nonmetal