Revision: Matter Around Us Science SSLC (English Medium) Class 8 Tamil Nadu Board of Secondary Education

• Matter is defined based on its physical and chemical structure. It occupies space and has mass, particularly as opposed to energy.
• Atoms and molecules are the building blocks of matter, consisting of positively charged protons, neutral neutrons, and negatively charged electrons, respectively.

Atom — An atom is the smallest part of an element that takes place in a chemical reaction.

Matter—Anything that has mass and occupies space is called matter.

Anything that has mass and occupies space is called matter.

An emulsion is a colloid in which minute droplets of one liquid are dispersed in another liquid which is not miscible with it. Examples are milk and butter.

Chemical properties of matter tell us how a substance changes when it interacts with other substances. These properties describe how matter reacts and forms new substances. When a chemical change happens, the matter changes into something new. The atoms in a substance rearrange themselves, and a new substance is formed. For example:

• When wood burns, it turns into ash and smoke.
• When iron is exposed to air and water, it forms rust.

Examples of Chemical Properties:

• Flammability: This describes if a substance can burn. For example, wood is flammable because it can catch fire.
• Reactivity: This tells us how a substance reacts when mixed with others. For example, if you mix vinegar with baking soda, they react to create bubbles.
• Rusting: Some metals, like iron, will form rust when they come in contact with water and air.
• Acidity and Basicity: Some substances are acidic (like lemon juice), while others are basic (like soap). Acids and bases can react with each other to form new substances.

The matter is defined as anything that has mass and takes up space. The matter is found in solid, liquid and gas.

It is a state of matter which has only definite mass but no definite shape and volume. It takes up the shape of the container
e.g. – Carbon dioxide, oxygen, etc.

The amount of space occupied by a matter is called its volume.

The process by which matter changes from one state to another and back to original state, without any change in its chemical composition.

Molecule — A molecule is a smallest part of a compound that exists independently.

It has a definite mass and volume but lacks a shape of its own. It takes up the shape of the containing vessels. It can be compressed to an extent,
e.g. – Milk, water, ink, etc.

Mass is the quantity of matter contained in the body.

A solid is that state of matter which has a fixed shape, mass, and volume. It suffers very small changes in volume by changing the temperature. It can not be compressed.
e.g. – Sand, Wood, Copper, Ice, etc.

Intermolecular force — The force of attraction between the molecules of a given substance is called intermolecular force.

The process by which matter changes from one state to another and back to the original state, without any change in its chemical composition.

Anything that has mass and occupies space is called matter.

Element is a substance which cannot be broken further into simpler substances and has a definite set of properties. Elements are made up of only one kind of atoms.

Formula: Formula is a short way of representing the molecule of an element or a compound

Atom: An atom is the smallest indivisible unit of an element which exhibits all the properties of that element and may or may not have an independent existence. An atom is the smallest indivisible unit of an element which exhibits all the properties of that element and may or may not have an independent existence. 

Element is a substance which cannot be split up into two or more simple substances by usual chemical methods of applying heat, light or electric energy; for example, hydrogen, oxygen and chlorine.

Molecule: A molecule can be defined as the smallest unit of an element or a compound which exhibits all the properties of that element or compound and has an independent existence. They are divisible into atoms.

Compounds are pure substances composed of two or more elements in definite proportion by mass and has properties, entirely different from those of its constituents elements.
Compound, are made up of different types of atoms combined chemically.

Elements: An element is defined as a pure substance made up of only one kind of atoms that cannot be converted into anything simpler than itself by any physical or chemical process. 

“Mixtures can be defined as. a kind of matter which is formed by mixing two or more pure substances (elements and compounds) in any proportion, such that they do not undergo any chemical change and retain their individual properties. Therefore they are impure substances.

The number of atoms in a molecule of an element is called its atomicity. 

Elements : An element is the basic form of matter that cannot be broken down into simpler substances by chemical reactions.

Compounds : A compound is a pure substance formed by the chemical combination of two or more elements in a fixed ratio by mass.

Alchemy was a form of chemistry studied in the middle age, which was concerned with trying to discover ways to change ordinary metals into gold.

Non-metals, except hydrogen, are the elements which form negative ions by the gain of electrons.

Certain elements which show properties of both metals and non metals are called metalloids or semi-metals.

Compounds: Compounds are pure substances composed of two or more elements in definite proportion by mass and has a definite set of properties. The compound is made up of only one kind of molecules

Carbonic acid

• Metals are mostly solids at room temperature; mercury and gallium are exceptions and exist in liquid form.
• Metals have a shining surface called metallic lustre, which may decrease due to oxidation or reaction with gases.
• Malleability allows metals to be beaten into thin sheets (gold and silver are highly malleable), and ductility allows them to be drawn into wires (gold is the most ductile).
• Metals are good conductors of heat and electricity, with silver and copper being excellent conductors.
• Most metals are hard with high melting and boiling points, but alkali metals (sodium, potassium) are soft and low‑melting, and metals are sonorous, producing sound when struck.

• Most metals are solids at room temperature, but mercury is a liquid, and gallium and caesium melt in the palm of the hand due to their very low melting points.
• Alkali metals (lithium, sodium, potassium) are soft, low-density metals with low melting points, unlike most metals.
• Iodine, though a non-metal, shows a metallic lustre, which is unusual for a non-metal.
• Carbon exists in allotropes: diamond is the hardest natural substance, and graphite is a good conductor of electricity.
• Nonmetals are usually non-lustrous, soft, poor conductors, and exist in solid or gas states, with bromine being the only liquid non-metal.