Revision: The Language of Chemistry Chemistry (English Medium) ICSE Class 9 CISCE

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

• 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.

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.

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.

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

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. 

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.

Atomic number— Atomic number refers to the number of protons present in an atom. It is denoted by Z.

Mass number : Numbr of protons and neutrons present in the nucleus of an atom.

Atomic number : Number of protons present in the nucleus of an atom.

Atomic weight : It is the ratio that tells how many times an atom of an element is heavier than atom of Hydrogen

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.

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

When the properties of elements in a period or a group of the modern periodic table are compared, certain regularity is observed in their variations. It is called the periodic trends in the modern periodic table.

The valency of an element is determined by the number of electrons present in the outermost shell of its atoms, that is, the valence electrons.

Valency denotes the combining capacity of the atom of an element. It is equal to the number of electrons an atom can donate or accept or share.

Electrons revolve around the nucleus in certain definite circular paths called orbits or shells. 

A chemical equation is a balanced account of a chemical transaction. It is not merely a qualitative statement, but it also gives quantitative information of a chemical reaction.

OR

The representation of a chemical reaction in a condensed form using chemical formulae is called as the chemical equation.

The reactions in which heat is absorbed are called endothermic reactions. The reactants absorb heat for form products.

It is the sum of total number of protons and neutrons present in a nucleus.

1. atomic mass number = number of protons + number of neutrons.
2. Atomic number = number of protons = number of electrons. It is denoted by Z.
3. Mass number = number of protons + number of neutrons. It is denoted by A.
4. For example: Carbon atom its,
   1. Number of proton = 6
   2. Number of neutrons = 6
   3. Number of electron = 6
5. Atomic number (Z) = number of protons = number of electrons = 6.
6. Mass number (A) = number of proton + number of neutrons = 6 + 6 =12.

A mass unit equal to exactly one-twelfth `(1/12^(th))` the mass of one atom of carbon-12 is called one atomic mass unit. It is written as ‘u’.

The empirical formula mass is the sum of atomic masses of various elements present in the empirical formula.

The empirical formula of a compound is the simplest formula, which gives the simplest ratio in whole numbers of atoms of different elements present in one molecule of the compound.

catalytic hydrogenation is a process by which hydrogen gas is passed through vegetable oils in the presence of catalyst like Ni, Pt or Pd to convert them into solid vanaspati ghee.

Carbonic acid

• Word equations use names; chemical equations use formulas.
• Reactants → Products, with arrow showing reaction direction.
• Use + between two or more reactants or products.
• Show states: (s), (l), (g), (aq); use ↑ for gas, ↓ for precipitate.
• Heat (Δ) or other conditions go above/below the arrow.

• Law of Conservation of Mass: In a chemical reaction, mass is neither created nor destroyed, so the number of atoms of each element must be equal on both sides.
• A skeletal (unbalanced) equation has unequal atoms of one or more elements on the LHS and RHS.
• Balancing is done using the hit-and-trial method, starting with the compound having the most atoms and balancing hydrogen and oxygen last.
• Only coefficients are changed while balancing; chemical formulas must not be altered.
• A balanced equation may also indicate physical states (s, l, g, aq) and reaction conditions, such as temperature, pressure, or a catalyst.