Atoms, Elements & Compounds

Question 1

Elements VS Compounds VS Mixtures

Answer 1

• Elements:
  Pure substances composed of only one type of atom.

Cannot be broken down into simpler substances by chemical means.

Have specific properties unique to each element.

• Compounds:
  Pure substances composed of two or more different types of atoms chemically bonded together.

Can be broken down into simpler substances by chemical reactions.

Have properties distinct from the elements that compose them.

• Mixtures:
  Combinations of two or more substances physically mixed together.

Components retain their individual properties and identities.

Can be separated by physical means (e.g., filtration, distillation).

Question 2

Isotopes
- Definition
- Calculate Atomic Mass and abundance of isotopes

Answer 2

Isotopes are different atoms of the same element that have the same number of protons but different numbers of neutrons

Isotopes of the same element have the same chemical properties because they have the same number of electrons and therefore the same electronic configuration

To calculate the relative atomic mass of an element from the relative masses and abundances of its isotopes:

1. Multiply each isotope’s mass by its abundance (as a decimal).
2. Sum up the products obtained from step 1.
3. Divide the sum by 100 to normalize the result.

Question 3

Ionic Bonding

Answer 3

An ionic bond is a strong electrostatic attraction between oppositely charged ions

The giant lattice structure of ionic compounds is a regular arrangement of alternating positive and negative ions

Ionic bonding usually occurs between metal and non-metals

Question 4

Formation of Cations (+) and Anions (-)

Answer 4

Formation of Cations ( + Ions):

Cations are formed when atoms lose one or more electrons.

Atoms lose electrons to achieve a stable electron configuration, typically by attaining a noble gas configuration (full outer shell).

Loss of electrons results in a net positive charge on the ion due to the excess of protons compared to electrons.

Cations are typically formed by metals.

• Formation of Anions ( - Ions):

Anions are formed when atoms gain one or more electrons.
Atoms gain electrons to achieve a stable electron configuration, typically by filling their outer electron shells.

Addition of electrons results in a net negative charge on the ion due to the excess of electrons compared to protons.

Anions are typically formed by nonmetals.

Question 5

Characteristics of Ionically Bonded Compounds

Answer 5

• High Melting and Boiling Points:

Ionic compounds consist of ions held together by strong electrostatic forces of attraction, known as ionic bonds.

These bonds require a significant amount of energy to break, leading to high melting and boiling points.

In the solid state, ions are arranged in a regular lattice structure, which further contributes to the stability of the compound.

• Good Electrical Conductivity in Aqueous or Molten State, Poor when Solid:

In the solid state, ions are held in fixed positions within the lattice structure and cannot move freely.

Therefore, solid ionic compounds do not conduct electricity because there are no mobile charge carriers.

In the molten or aqueous state, ions are free to move and conduct electricity due to the presence of mobile charge carriers.

Question 6

Covalent Bonding

Answer 6

A covalent bond is formed when a pair of electrons is shared between two atoms leading to noble gas electronic configurations

Question 7

Covalent Bonding Characteristics

Answer 7

• Low Melting Points and Boiling Points due to Weak Intermolecular Forces:

Simple molecular compounds consist of discrete molecules held together by weak intermolecular forces.

These intermolecular forces are much weaker than ionic or covalent bonds.

Weak intermolecular forces result in low melting and boiling points because less energy is required to overcome these forces and break the molecules apart.

Molecules are easily separated from each other, leading to their low melting and boiling points.

• Poor Electrical Conductivity:

Simple molecular compounds do not contain charged particles (ions) or free-moving electrons.

As a result, they do not conduct electricity in any state (solid, liquid, or gas) because there are no mobile charge carriers available to carry an electric current.

Question 8

Graphite
- Structure
- Properties
- Uses

Answer 8

• Structure:

Consists of layers of carbon atoms arranged in hexagonal rings.

Each carbon atom forms three covalent bonds with neighboring atoms within its layer, creating a flat, two-dimensional structure.

• Properties:

Soft and slippery due to the weak forces between layers.

Good conductor of electricity along the planes of carbon atoms due to delocalized electrons.

High melting point due to strong covalent bonds within layers.

• Uses:

Lubricant: The layers in graphite can slide over each other easily

Electrode because it is inert

Question 9

Diamond
- Structure
- Properties
- Uses

Answer 9

• Structure:

Each carbon atom forms four covalent bonds with neighboring atoms in a tetrahedral arrangement.

Forms a three-dimensional network structure, with each carbon atom bonded to four other carbon atoms in a strong, rigid lattice.

• Properties:

Extremely hard and rigid due to the strong covalent bonds throughout the structure.

Does not conduct electricity as there are no free electrons or ions.

Very high melting point due to the strong covalent bonds in all directions.

• Uses:

hardness and rigidity give its ability to withstand high pressures and maintain sharp edges.

Question 10

Silicon Dioxide
- Structure
- Properties

Answer 10

• Structure:

Each silicon atom forms four covalent bonds with four oxygen atoms, and each oxygen atom forms two covalent bonds with silicon atoms.

Forms a three-dimensional network structure similar to diamond but with alternating silicon and oxygen atoms.

• Properties:

Hard and rigid structure similar to diamond.

Does not conduct electricity as there are no free electrons or ions.

High melting point due to the strong covalent bonds in all directions.

Question 11

Metallic Bonding

Answer 11

Metallic bonding is the electrostatic attraction between the positive ions in a giant metallic lattice and a ‘sea’ of delocalised electrons

Question 12

Properties of Metals

Answer 12

Good Electrical Conductivity:
Delocalized electrons allow for efficient movement of charge.

Free electrons enable metals to conduct electricity effectively.

Malleability and Ductility:
Metals have closely packed lattice structures.

Layers of atoms can slide over each other.

Malleability: Metals can be hammered or rolled into thin sheets without breaking.

Ductility: Metals can be drawn into thin wires due to the stretching and alignment of atoms.