Atoms and Molecules

Atoms and Molecules

manmohan singh

atoms

Atom, smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element.

Molecules

A molecule is the smallest particle in a chemical element or compound that has the chemical properties of that element or compound. 

Molecules are made up of atoms that are held together by chemical bonds. These bonds form as a result of the sharing or exchange of electrons among atoms.

Structure of Atom

Atoms consist of three basic particles: protons, electrons, and neutrons. The nucleus (center) of the atom contains the protons (positively charged) and the neutrons (no charge). The outermost regions of the atom are called electron shells and contain the electrons (negatively charged).

Laws of chemical combination

(by Lavoiser and josph l .Proust)

• laws of chemical combination

• law of conservation of mass

Law of chemical Combination

1) Law of conservation of mass :- The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction.

For example, when wood burns, the mass of the soot, ashes, and gases equals the original mass of the charcoal and the oxygen

law of coservation of mass

exapmle by image

law of constant proportion

The law of constant proportions states that chemical compounds are made up of elements that are present in a fixed ratio by mass. ... For example, in a nitrogen dioxide (NO₂) molecule, the ratio of the number of nitrogen and oxygen atoms is 1:2 but the mass ratio is 14:32

Atomic mass

Atomic mass refers to the mass of an atom. It depicts how many times an atom of an element is heavier than one-twelth (1/12^th) the mass of one atom of carbon-12 of mass of one carbon atom.

Atomicity

• Atomicity can be defined as the total number of atoms that composes a molecule. Simply put, it is the no of atoms present in a molecule. For example, each molecule of oxygen is composed of two oxygen atoms.

what is an ion?

Metals and non-metals leads to the formation of Compounds that possess charged species. These charged species are called ions. These charged species can be either positively charged called cation or negatively charged called anion. ... Ions possessing more than one atom are termed as polyatomic ions.

Atomic mass unit

An atomic unit of mass is defined as accurately 1/12 the mass of a carbon-12 atom. The carbon-12 atom has six neutrons and six protons in its nucleus. The atomic unit mass is symbolized as AMU or amu.

1 AMU = Average of the proton rest mass and the neutron rest mass.

1 AMU = 1.67377 x 10 -27 kilogram or 1.67377 x 10 -24 gram.

Atomic number

The atomic number of an atom is equal to the number of protons in the nucleus of an atom or the number of electrons in an electrically neutral atom. For example, in a sodium atom, there are 11 electrons and 11 protons. Thus the atomic number of Na atom = number of electrons = number of protons = 11.

writing molecular formula

Molecular Formula: The molecular formula of a compound is the symbolic representation of its molecules.Writing the Chemical Formula of a CompoundTo write the chemical formula of a compound, the following information should be available:(i) Symbols of the elements or radicals which constitute the compound(ii) Valencies of the elementsThe method applied for writing the chemical formula is called the criss-cross method.

Mass number

Mass number of an atom is defined as the sum of the number of protons and number of neutrons. Mass number is nearly equal to the atomic mass of an atom. Since, protons and neutrons reside in the nucleus, thus they are also known as nucleons.

_{chemical formula}

_{A chemical formula shows the elements that make up the compound and the numbers of atoms of each element in the smallest unit of that compound, be it a molecule or a formula unit.}

_{Knowing the names of the elements and a few basic rules allows us to name simple compounds given the chemical formula. We also can reverse the process. That is, if we know the name of the compound, we should be able to write the chemical formula.}

molecular mass

The molecular mass of a substance is relative mass of its molecules as compared with mass of C-12 atom taken as 12 units. or. The molecular mass is equal to sum of its atomic masses of all the atoms present in one molecule of substance

mole concept

What is the Mole Concept?The mole concept is a convenient method of expressing the amount of a substance. Any measurement can be broken down into two parts – the numerical magnitude and the units that the magnitude is expressed in. For example, when the mass of a ball is measured to be 2 kilograms, the magnitude is ‘2’ and the unit is ‘kilogram’.

Thanks

The End