UNIT 2 Atoms Elements and Compounds

Elements

A substance made of atoms that all contain the same number of protons which cannot be broken down into anything simpler through chemical means

Compounds

A substance made of two or more different elements chemically bonded in a fixed ratio requiring a chemical reaction to separate

Mixture

Two or more substances that are physically mixed but not chemically combined. Can be separated by physical means

Compounds vs Mixture

1. Compounds can only be separated by chemical means while mixtures can be separated by physical means 2. Compounds have different properties from the elements in it while mixtures keep the properties of its parts 3. Compounds have a fixed ratio while mixtures can be in any ratio throughout it

Proton

Positive subatomic particle found in the nucleus with a relative mass of 1

Nuetron

Neutral subatomic particle found in the nucleus with a relative mass of 1

Electron

Negative subatomic particle found in the shells with a relative mass of 1/1840 (negligible)

Proton Number/ Atomic Number

Amount of protons

Mass number

Protons + Neutrons

Electron shell maximum

Shell 1: 2

Shell 2: 8

Shell 3: 8

Atomic configuration of element with 17 electrons

2,8,7

Group number

Vertical column, amount of electrons in outer shell

Period number

Horizontal rows, amount of occupied shells

Why are Group 8 unreactive

Full outer shell Don't need to lose or gain electrons

Isotopes properties

Same chemical properties as they have the same electronic configuration

Different physical properties as they have different masses due to different amount of neutrons in the nucleus

Relative atomic mass formula

Ar = (mass of isotope 1 x abundance + mass of isotope 2 x abundance)/100

Ionic Bonding

Strong electrostatic attraction between oppositely charged ions

Anions

Negative ions

Giant lattice structure of ionic compounds

Regular arrangement of alternating positive and negative ions

Ammonia

NH3

Properties of Simple Covalent Bonds and why?

1. Low melting/boiling point: Only weak intermolecular forces, easy to overcome, little energy needed 2. Poor conductors of electricity: No free moving ions or delocalised electrons to carry charge

Graphite Structure

1. Each carbon joined to 3 others 2. Flat hexagonal layers 3. Layers can slide over each other

Graphite Properties

1. Conducts electricity (has delocalised electrons) 2. Soft and slippery (weak intermolecular forces in between layers allow layers to slide over each other) 3. High melting/boiling point (strong covalent bonds need lots of energy to overcome)

Diamond Structure

1. Tetrahedral 2. Each carbon joined to 4 others 3. Covalent bonds throughout

Diamond Properties

1. Extremely hard (each atom locked in place by strong covalent bond) 2. Very high melting/boiling points (strong covalent bonds difficult to overcome) 3. Does not conduct electricity (no delocalised electrons or free moving ions to carry charge)

Silicon Oxide Structure

1. Each silicon bonded to 4 oxygen 2. Each oxygen bonded to 2 silicon 3. Tetrahedral

Uses of Diamond

Industrial cutting tools

Metallic Bonding

The electrostatic attraction between positive ions in a giant metallic lattice and a sea of delocalised electrons

Properties of metals and why?

1. Good conductors of electricity (delocalised electrons) 2. Malleable and ductile (metals are arranged in layers which can slide over each other without breaking the metallic bonds)

Ductile

Can be easily drawn out into wires

Ammonia vs Ammonium

Ammonia is NH3 (ends in -a, like air it is a gas)

Ammonium is NH4^+ (ends in -um like Sodium or Potassium)