Atoms, Elements and Compounds

What is an element?

A pure substance made of only one type of atom that cannot be broken down into simpler substances by chemical means.

Give an example of an element.

Oxygen (O₂), Iron (Fe), Neon (Ne).

What is a compound?

A pure substance formed when two or more different elements are chemically combined in a fixed ratio.

Give an example of a compound.

Water (H₂O), Sodium Chloride (NaCl).

What is a mixture?

A combination of two or more substances that are not chemically combined, with varying composition.

Give an example of a mixture.

Air, Saltwater, Sand and Iron Filings.

How can mixtures be separated?

By physical methods such as filtration and distillation.

Describe the particle diagram of an element.

Identical atoms are represented as [O] [O] [O].

Describe the particle diagram of a compound.

Different atoms bonded are represented as [H-O-H] [H-O-H].

Describe the particle diagram of a mixture.

Different particles that are not bonded are represented as [O] [Na] [Cl].

What is the structure of an atom composed of?

A small, central nucleus containing protons and neutrons, with electrons orbiting in shells.

What charge and mass does a proton have?

Relative Charge = +1, Relative Mass = 1.

What charge and mass does a neutron have?

Relative Charge = 0, Relative Mass = 1.

What charge and mass does an electron have?

Relative Charge = -1, Relative Mass ≈ 0 (1/1840).

What is the atomic number (Z)?

The number of protons in the nucleus.

What is the mass number (A)?

The total number of protons and neutrons in the nucleus.

How do you calculate the number of neutrons in an atom?

Number of neutrons = Mass Number (A) - Atomic Number (Z).

What does standard notation for sodium look like?

Mass Number (A) = 23, Sodium (Na), Atomic Number (Z) = 11.

What is electronic configuration?

The distribution of electrons in the atomic shells.

What is the maximum number of electrons in the first shell?

The first shell holds a maximum of 2 electrons.

What is the maximum number of electrons in the second and third shells?

Both the second and third shells hold a maximum of 8 electrons.

What is the electronic configuration of sulfur (Z=16)?

2.8.6.

What does Group Number indicate in the periodic table?

The number of outer shell electrons (for Groups I-VII).

What does Period Number indicate in the periodic table?

The number of occupied electron shells.

Why are Noble Gases unreactive?

They have a full outer shell of electrons.

What is an isotope?

Atoms of the same element with different numbers of neutrons.

Give an example of isotopes.

Chlorine-35 (17p, 18n) and Chlorine-37 (17p, 20n).

Do isotopes have the same chemical properties?

Yes, they have identical chemical properties because they have the same electronic configuration.

Do isotopes have different physical properties?

Yes, they can differ in density, rate of diffusion, etc.

What does relative atomic mass (Aᵣ) report?

The weighted mean mass of all the isotopes of an element.

What is the formula to calculate Aᵣ?

Aᵣ = ( (% iso1 × mass iso1) + (% iso2 × mass iso2) ) / 100.

Calculate the relative atomic mass of Boron with isotopes B-10 (20%) and B-11 (80%).

Aᵣ = 10.8.

What are ions?

Charged particles formed when atoms lose or gain electrons.

What is a cation?

A positive ion formed when a metal atom loses electrons.

Give an example of a cation.

Na → Na⁺ + e⁻.

What is an anion?

A negative ion formed when a non-metal atom gains electrons.

Give an example of an anion.

Cl + e⁻ → Cl⁻.

What is an ionic bond?

The strong electrostatic attraction between oppositely charged ions.

How is an ionic bond formed?

Through the transfer of electrons from a metal to a non-metal.

What is a dot-and-cross diagram?

A diagram used to represent the electron distribution of atoms in ionic or covalent bonds.

What structure do ionic compounds form?

A giant ionic lattice.

What are the properties of ionic compounds?

High melting/boiling points, conduct electricity when molten/dissolved, do not conduct when solid, and are brittle.

What defines a covalent bond?

A shared pair of electrons between two non-metal atoms.

Give an example of a simple covalent molecule.

Hydrogen (H₂).

Show the dot-and-cross diagram for water (H₂O).

H
•
O•••
•
H.

What type of bond is present in oxygen (O₂)?

A double bond.

What are the properties of simple covalent molecules?

Low melting/boiling points, do not conduct electricity, often gaseous or liquid at room temperature.

What are giant covalent structures?

Huge networks of atoms bonded together by strong covalent bonds.

What is the structure of diamond?

Each carbon atom is covalently bonded to four other carbon atoms in a rigid tetrahedral structure.

Why is diamond very hard?

Due to strong bonds and a rigid structure.

What are the properties of graphite?

Soft & slippery, high melting point, conducts electricity and heat.

What is Silicon(IV) Oxide (Silica)?

Each silicon atom is bonded to four oxygen atoms; it is hard with a high melting point.

What is metallic bonding?

The electrostatic attraction between positive metal ions and delocalised electrons.

How are positive metal ions arranged in metallic bonding?

In a giant lattice.

What are the electrical and thermal conductivity properties of metals?

Good conductivity due to free-moving delocalised electrons.

Why are metals malleable and ductile?

Positive ions can slide over each other without breaking the structure.

What are the melting and boiling points of metals like?

High melting and boiling points due to strong attractions between ions and electrons.