Chemistry Topic 2 - Combining Atoms

What determines the physical properties of an element?

Structure and Bonding

What are the 3 different ways atoms need to be arranged?

Monatomic - Single Atom.

Molecules - A cluster of 2 or more atoms bonded together.

Lattice - A regular repeating arrangement of atoms and ions bonded in a fixed ratio.

What is the difference between intermolecular bonding and intramolecular bonding.

Intermolecular bonding involves the bonding within a molecule or lattice. Whereas intramolecular bonding is the bonding between molecules.

Why does bonding occur?

Due to the forces of attraction between oppositely charged particles

What are the 4 types of intramolecular bonding and what types of atoms bond within them.

Ionic - Between a non-metal and metal atom

Metallic - Between metal atoms

Covalent molecular - Between non-metal atoms forming a molecule

Ionic Continuous - Between non-metal atoms forming a lattice

What is ionic bonding?

Between non-metals and metal atoms, electron lost by metal atom is picked up by non-metal atom forming an anion(-) and cation(+)

What is metallic bonding?

Metal atoms lose their electrons easily to be cations(+) where they are arranged together in lattice structures where the electrons are delocalized and move freely between the cations.

The force of attraction between the delocalized electrons (-) and cations (+) then form a metallic bond

What is covalent bonding and the difference continuous and molecular.

Covalent bonding is between non-metal atoms where they share electrons to reach a full outer shell, the attraction of electrons (-) to the nucleus (+) creates the covalent bond. Molecular is where it bonds to together to form a molecule, however in continuous this happens in a continuous way the atoms arrange together in a lattice.

What occurs in Exothermic and Endothermic Reactions?

Exothermic - Energy is being released from the molecule allowing bonds to be made.

Endothermic - Energy is used to overcome the attractive forces of particles.

How does the melting point vary between Intramolecular and Intermolecular bonds (referring to strength of attraction)

Intramolecular bonds have a higher melting points, as more energy is required to overcome the attractive force and separate molecules to form a liquid.

Intermolecular bonds have weaker strength of attraction therefore have a lower melting point due to less energy required to separate molecules.

What kind of melting point does Ionic, metallic and covalent (continuous) materials have (referring to forces between particles)

They have a high melting point due to strong intramolecular forces thus more energy is required to break the forces between particles.

What kind of melting point does covalent (molecular) molecules have?

They have a low melting point due to weak intermolecular forces causing less energy needed to separate molecules.

What makes a material a conductor

When they have charged and moving particles

What are Non-Polar covalent bonds

Where the electronegativity of atoms bonding is the same, therefore the electrons are shared equally.

What are Polar Covalent Bonds

Where the electronegativity of atoms is not the same when bonding, therefore the electrons are shred equally.

What occurs in the electron cloud diagram

It is more skewed around the more electronegative atom.

What are the electronegativity difference values that determine non-polar, polar, and ionic bonds.

> 0.5 = Non-Polar

0.5 - 2 = Polar

• 1.6 - 2 (Ionic if involves metal)

2+ = Ionic

What makes a molecule non-polar

1. Each bond in the molecule is non-polar

2. No unbonded electron pairs

3. Each bond in the molecule has the same polarity.

What make a molecule polar

1. Bonds can be non-polar, however there is unbonded electron pairs

2. Bonds in the atom have different polarities

Explain dipole moment and what it is like in non-polar and polar molecules

It is a vector quantity (magnitude and direction) of the polarity within a molecule.

Non-polar: Dipole moments are all symmetrical therefore they cancel out causing a symmetrical shape

Polar: The arrow points to the more electronegative moment therefore the dipole moments are asymmetrical and don’t cancel. This causes there to be a net dipole moment

In bent molecules like H₂O the Oxygen is more electronegativity compared to the hydrogen therefore pulling away and causing a bent shape.

What is a compound?

Consists of atoms connected by chemical bonds in a fixed ratio

What is Molecular formula compared to empirical formula

Molecular formula shows the exact amount of atoms present within a molecule, where as empirical formula shows the simplified whole number ratio of elements in a molecule

How to determine the percentage mass of a element within a compound

1. Times the atomic mass of the element by the amount of atoms of that element.

2. Divide that by the overall mass of the molecule.

3. Times by 100 to get the percentage.

How to find molecular formula on a compound (known molar mass)

Times the percentage of each element by the mass of the compound to find the mass of each element in gmol^-1.

Divide the mass (grams) of each element by its atomic mass

Put together to form the molecular and formula and simplify if needed for the empirical formula (round to whole number).

How to find molecular formula on a compound (unknown molar mass)

Times the percentage of each element by a assumed compound mass of 100g to find the mass of each element in grams.

Divide the mass (grams) of each element by its atomic mass

Put together to form the molecular and formula and simplify if needed for the empirical formula (round to whole number).