Atoms and Molecules

An atom is the smallest unit of matter that makes up a chemical element. Every solid, liquid, gas, and plasma is made up of neutral or ionised atoms. Atoms are extremely small, measuring about 100 picometers in diameter. 

This article will study atoms, molecules and ions, the difference between atom and molecule and molecular elements in detail.

Atoms Molecules and Ions

Atoms and Molecules Definition

Every atom is made up of a nucleus and one or more electrons attached to it. One or more protons and a number of neutrons make up the nucleus. Only one type of hydrogen, the most prevalent, lacks neutrons. The nucleus contains more than 99.94% of an atom's mass. Protons have a positive electric charge, while electrons have a negative charge and neutrons don't have any. The atom is electrically neutral if the number of protons and electrons is equal. 

The nucleus is made up of neutrons and protons, which are responsible for an atom's weight and positive charges. A neutron is a neutral particle with a mass of one unit. A proton is a particle with a single positive charge and a mass of one unit. The number of protons or positive charges in the nucleus determines an element's atomic number. The total number of protons and neutrons in the nucleus is used to calculate an element's atomic weight. A single negative charge is carried by an electron. To have zero charge, an element's atom must have the same amount of protons as electrons. Like the layers of an anion, these electrons are organised in orbits around the nucleus of the atom. Atoms combine to form molecules.

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Ions 

When an atom contains more or fewer electrons than protons, it has a negative or positive overall charge, and these atoms are known as ions.

Size of an Atom

An atom is exceedingly small, much smaller than our imagination allows us to imagine. When more than millions of atoms are packed together, a layer of an atom the thickness of a thin sheet of paper is created. Because it's difficult to detect the positions of electrons surrounding the nucleus, measuring the size of an isolated atom is impossible.

However, assuming that the distance between neighbouring atoms is equal to half the radius of an atom, the size of an atom can be approximated. The radius of an atom is usually measured in nanometres.

1 m = 109nm

Structure of an Atom

An atom is made up of three particles: neutrons, protons, and electrons, with the exception of hydrogen, which has no neutrons.

1. Every atom contains a nucleus that is surrounded by one or more electrons.

2. The nucleus usually has the same amount of protons and neutrons, collectively referred to as nucleons.

3. Protons have a positive charge, while electrons have a negative charge, and neutrons have no charge.

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Dalton's Atomic Theory 

Dalton's atomic theory has certain strange features:

1. Matter is made up of atoms, which are extremely small and indivisible particles that cannot be generated or destroyed.

2. An element's atoms are identical in every way, including size, mass, density, and chemical characteristics, but they differ from atoms of other elements.

3. A tiny number of atoms of an element unite to form molecules of the element.

4. Compound molecules are formed when atoms of one element interact with atoms of another element in a simple whole-number ratio.

5. Atoms are the smallest units of matter that can participate in a chemical reaction involving solely atom rearrangement.

What is Atomic Mass?

In simple terms, “atomic mass”, is the quantity of matter contained in an atom of an element. It is expressed as a multiple of one-twelfth the mass of the carbon-12 atom, 1.992646547 × 10⁻²³ grams, which is assigned an atomic mass of 12 units. In this scale 1 atomic mass unit (amu) corresponds to 1.660539040 × 10⁻²⁴ gram. The observed atomic mass is roughly equal to the sum of the masses of the protons, neutrons, and electrons that make up the atom. A single neutron or proton has a weight very close to 1 amu. Electrons are much smaller in mass than protons, only about 1/1800 of an atomic mass unit, so they do not contribute much to an element’s overall atomic mass.

Scientists determine the atomic mass by calculating the mean of the mass numbers for its naturally-occurring isotopes. The list below illustrates the charges and the masses of the subatomic particles:

Masses of Subatomic Particles

The number of protons determines an element’s atomic number (Z) and distinguishes one element from another. Here are some elements, from atomic number 1-20, with their atomic masses:

Atomic Masses of Some Elements

Given an atomic number (Z) and mass number (A), it is easy to find the number of protons, neutrons, and electrons in a neutral atom. For example, a lithium atom (Z=3, A=7 amu) contains three protons (found from Z), three electrons (as the number of protons is equal to the number of electrons in an atom), and four neutrons (7 – 3 = 4).

Molecule 

A molecule is a chemically bonded group of two or more electrically neutral atoms. Molecules, unlike ions, do not have an electrical charge. 

In the kinetic theory of gases, the term molecule is widely used to refer to any gaseous particle, regardless of composition. Noble gases are single atoms, which contradicts the traditional definition of a molecule, which specifies that it must include two or more atoms.

Molecules are common components of matter. They also make up the vast majority of the world's oceans and atmosphere. Molecules make up the majority of organic compounds. Molecules are the building blocks of life, such as proteins, amino acids, nucleic acids (DNA & RNA), sugars, carbohydrates, lipids, and vitamins. Iron sulfate is an example of a nutritional mineral that is not a molecule.

Bonding in Molecules 

Molecular elements exhibit two types of bonding:

It can be covalent or ionic.

Covalent Bonding

A covalent bond is a chemical relationship that involves the sharing of electron pairs between atoms. Shared pairs or bonding pairs are the stable balance of attractive and repulsive forces between atoms when they share electrons, while covalent bonding is the stable balance of attractive and repulsive forces between atoms when they share electrons.

Ionic Bonding 

The major interaction in ionic compounds is ionic bonding, which is a sort of chemical bond involving the electrostatic attraction between oppositely charged ions. Atoms that have lost one or more electrons (cations) and atoms that have gained one or more electrons (anions) make up the ions (termed anions)

Chemical Formula 

A molecule's chemical formula is made up of one line of chemical element symbols, numbers, and additional symbols like parentheses, dashes, brackets, and plus (+) and minus (-) marks. There is a maximum of one typographic line of symbols, including subscripts and superscripts.

The empirical formula of a compound is a very basic type of chemical formula. It's the most basic integer ratio of the chemical elements that make it up. 

Example of a Water Molecule

Water, for example, always has a 2:1 ratio of hydrogen to oxygen atoms, and ethanol (ethyl alcohol) always has a 2:6:1 ratio of carbon, hydrogen, and oxygen. However, this does not indicate the kind of molecule; dimethyl ether, for example, has the same ratios as ethanol. Isomers are molecules that have the same atoms in various configurations. Carbohydrates, for example, have the same carbon:hydrogen: oxygen ratio (and consequently the same empirical formula), but differing total quantities of atoms in the molecules.

Empirical Formula 

The empirical formula of a compound is a very basic type of chemical formula. It's the most basic integer ratio of the chemical elements that make it up. Water, for example, always has a 2:1 ratio of hydrogen to oxygen atoms, and ethanol (ethyl alcohol) always has a 2:6:1 ratio of carbon, hydrogen, and oxygen. However, this does not indicate the kind of molecule; dimethyl ether, for example, has the same ratios as ethanol. Isomers are molecules that have the same atoms in various configurations. Carbohydrates, for example, have the same carbon:hydrogen: oxygen ratio (and consequently the same empirical formula), but differing total quantities of atoms in the molecules.

Difference Between Atom and Molecule

Chiral Carbon Definition

An asymmetric carbon atom (chiral carbon) is one that has four different sorts of atoms or groups of atoms linked to it. The Le Bel-van't Hoff rule states that the number of stereoisomers of an organic compound is 2n, where n is the number of asymmetric carbon atoms (unless there is an internal plane of symmetry); the most likely orientation of the bonds of a carbon atom linked to four groups or atoms is toward the apex (which involved a carbon atom bearing four different atoms or groups).

With the number of asymmetric carbon atoms, the maximum number of stereoisomers for any given molecule can be calculated as follows:

The greatest number of isomers = 2n where n is the number of asymmetric carbon atoms.

Did You Know?

The following are the most typical types of radioactive decay:

1. When the nucleus emits an alpha particle, which is a helium nucleus with two protons and two neutrons, the process is called alpha decay. A new element with a lower atomic number emerges as a result of the emission.

2. The weak force controls beta decay (and electron capture), which results from the transformation of a neutron into a proton or a proton into a neutron.

3. Gamma decay is caused by a change in the nucleus' energy level to a lower state, which leads to the emission of electromagnetic radiation.