Particulate Nature of Matter | Atomic Structure | Structure and Properties of Materials | The Particulate Nature of Matter

Lesson Objectives

• Atomic Structure
  • Atom
  • Structure of Atom
  • Identification of Element
  • Isotopes
  • Electronic Configuration
  • Periodic Table (intro)
• Structure and Properties of Materials
  • Elements
  • Molecules
  • Compounds
  • Mixtures and Compounds
  • Particle Models

Atomic Structure:

Atom:

An atom is the smallest possible particle of an element that can take part in a chemical change.

Structure of Atom:

Atoms are made up of three subatomic particles:

• Protons
  • Positively charged particles inside the nucleus of an atom.
• Neutrons
  • Neutral particles inside the nucleus of an atom.
• Electrons
  • Negatively charged particles which orbit the nucleus of an atom.

Properties of Subatomic Particles:

Arrangement of Particles in an Atom:

The diagram shows the arrangement of particles in a Lithium atom,

• Nucleus:
  • The protons and neutrons are held, tightly packed together, in the middle of an atom which is called the nucleus.
• Shell:
  • The electrons orbit around the nucleus in paths known as shells. These are the energy levels occupied by electrons.
• Valence shell:
  • The outer most shell is called the valence shell.
• Valence Electron:
  • The electrons in the valence shell are called valence electron.
• The size of the nucleus is very small as compared to the atom as the particles are held tightly together.
• We can never identify the exact position where the electron is orbiting at a given time as they move very rapidly.

Identification of Elements:

Nucleon Number/ Mass Number (A):

Nucleon Number is the number of particles inside the nucleus of an atom. This is the sum of an atom’s protons and neutrons.

Proton Number/Atomic Number (Z):

The proton number is the total number of protons in an atom. When an atom has no charge, the proton number is equal to the electron number as they cancel each other’s charges.

Identifying Elements:

All elements have a different proton number (Z) through which it can be identified.  The number of neutrons in an element can be found by subtracting the atomic number from the nucleon number. n = A-Z We can write the symbol of an element in the given form:

Isotopes:

• Isotopes are atoms of the same element, that have same number of protons but different number of neutrons.
• Isotopes are chemically identical as they have same atomic number, but they have different masses due to difference in the number of neutrons in the nucleus.
• For Example: carbon has three naturally occurring isotopes: Carbon-12, Carbon-13 and Carbon-14, with masses 12,13 and 14 respectively. Since each carbon isotope has a proton number of 6, the neutron number of the three isotopes is : 6,7 and 8.

Similarities and Differences Between Isotopes:

Isotopic Abundance:

Isotopic abundance is the percentage in which each isotope of an element exists in the environment naturally.

Relative Atomic Mass (Ar):

Relative atomic mass is the average mass of an atom. It is based on the isotopic abundance of the isotopes in the environment.

Calculating Relative Atomic Mass:

The formula for the relative atomic mass is to multiply all the isotopic masses to their abundance and divide it by hundred.  Example: There are two isotopes of chlorine, chlorine-35 and chlorine-37 meaning that they have masses of 35 and 37 respectively. Chlorine-35 has an isotopic abundance of 75% while Chlorine-37 has an isotopic abundance of 25%. Hence:  = 35.5 So, Chlorine has a relative atomic mass of 35.5.

Electronic Configuration:

Electronic configuration refers to the arrangement of electrons in the shells of an atom.

Valency:

Valency is the combining power of an atom. This is based on the electronic configuration of the electrons (shall be discussed later on in bonding).

General Formula:

• The general formula for calculating the electron capacity of each shell is:
  • 2n² where n is the number of electron shell
• According to the formula, the number of electrons is the first 3 shells should be:
  • 2 x 1 = 2 electrons: first shell
  • 2 x 2² = 8 electrons: second shell
  • 2 x 3² = 18 electrons: third shell
• The shells are numbered from the nucleus outwards.
• Although shell three should have 18 electrons according to the formula, the shells follow the octet rule which states that every atom wants to achieve stability by completing valence octet.
• As a result, the shell contains 8 electron and the rest of the electron move to the fourth shell of the atom.

Periodic Table:

We will discuss the periodic table in detail later on. However, a brief introduction is required at this point.

• Periodic table is a table that arranges all known elements in a particular pattern.
• The periodic table is read like a book from left to right.
• Each column is known as a group and each row is called a period.
  • The valence electron of each group is the group number itself. For example: in group 1, all elements have 1 valence electron.
  • The period number defines the number of shells.
• Metals are towards the left of the periodic table in groups 1,2 and 3.
• Non-metals are towards the right of the periodic table in groups 4,5,6, and 7.
• The inert or non-reactive gases are in the 8^th group and have a valence shell will 8 electrons.

First 20 Periodic Table Elements:

Structure and Properties of Materials:

Elements:

• An element is made up of atoms/molecules/ions chemically combined together which cannot be separated by chemical means.
• The periodic table has elements arranged in the order of increasing proton number.

Elements in Air:

The most common elements in air are:

• Nitrogen: 78%
• Oxygen: 21%

Elements in Earth’s Crust:

The Earth is made up of:

• Oxygen: 46.6%
• Other elements with Silicon (Si), Aluminum (Al), Calcium (Ca), Iron (Fe) making up about 90% of the remaining 53.4%.

Types of Elements:

Elements can be classified as:

• Naturally occurring elements:
  • There are 92 naturally occurring elements.
• Artificially prepared elements.

Molecules:

When two or more atoms chemically combine together, they form a molecule.

Types of Molecules:

• Diatomic Molecule:
  • When two atoms join together, they form a diatomic molecule e.g. Hydrogen (H₂), Carbon monoxide (CO), Oxygen (O₂)
• Triatomic Molecule:
  • When three atoms join together, they form a triatomic molecule e.g. Carbon dioxide (CO₂), Water (H₂O)
• Polyatomic Molecule:
  • When more than three atoms join to form a molecule, that molecule is called poly atomic molecule e.g. Sulfuric Acid (H₂SO₄)
• Homoatomic Molecule/ Molecule of an Element:
  • When atoms of the same element chemically join together, they form a homoatomic molecule e.g. H_2, O₂
• Heteroatomic Molecule/ Molecule of a Compound:
  • When atoms of different elements chemically join together, they form a heteroatomic molecule e.g. CO₂, H₂O

Compounds:

A compound is a pure substance that contains two or more different types of elements chemically combined together. For example, Carbon dioxide (CO₂), Ammonia (NH₃)

Base Particles:

• Smallest particle of Element: Atom
• Smallest particle of Compound: Molecule

Representation:

• To show the atoms present in the molecule, we use chemical symbols. Each element has a unique chemical symbol that can be used to identify it in an equation or compound.
• Chemical formula symbolizes the atoms in a compound.

Chemical Change:

When new compounds are formed as a result of a reaction, it is called a chemical change.s

Mixtures and Compounds:

Now that we know the meaning of both mixtures and compounds, here are a few differences between the two.

Particle Model:

The following diagram represents the particle models for atoms, molecules and mixtures.

Lesson Tags

Particulate Nature of Matter | Detailed Notes For Preparation & Revision | O Level Chemistry 5070 and IGCSE Chemistry 0620

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