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AS Chemistry Unit 1

An overview of ideas and definitions in AQA AS Chemistry (2420) Unit 1
by

Fraser Alcock

on 9 January 2014

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Transcript of AS Chemistry Unit 1

1st Ionisation Energy
The minimum energy required to remove one mole of electrons from one mole of atoms
in the gas state
. Is higher the stronger the electron is attracted to the nucleus
Electron shell /
Principle Energy Level
Ionisation
When an atom gains or loses an electron to become an ion. Metals tend to loose electrons to become + ions, non-metals gain electrons to become – ions
Ion
A charged particle, can be a single atom or a group of them eg. Ammonium ion NH4+
Isotope
Atom of same element with same number of protons and electrons but a different number of neutrons. Does not affect chemistry
AS Chemistry Unit 1
1 - Atomic Structure
Examples
1st Ionisation Energy of Sodium
Na → Na+ + e-


2nd Ionisation Energy of Zinc
Zn+ → Zn2+ + e-
Outer Shell /
Valence Shell
The outermost shell containing electrons. It is from here that electrons are gained and lost, and therefore where the chemistry happens
An orbit which electrons make around the nucleus
1st (K) Shell
Sub-shells: 1s

Electron capacity: 2
2nd (L) Shell
Sub-shells: 2s,2p

Electron capacity: 6
3rd (M) Shell
Sub-shells: 3s,3p,3d

Electron capacity: 18
4th (N) Shell
Sub-shells: 4s,4p,4d,4f

Electron capacity: 32
2 - Amount of Substance
Relative Atomic Mass (Ar)
Relative Molecular Mass (Mr)
Mass
(g)
Mr
(g/mol)
Moles
(mol)
Moles
(mol)
Volume
(dm^3)
Conc.
(moldm^-3)
A Mole
Avogadro’s Number (6.02x10^23) of particles
Molecular Formula
Actual number of each atom in a molecule
Empirical Formula
Simplest possible integer ratio of atoms in a molecule
Displayed Formula
The 2 dimensional arrangement of atoms in a compound, with all bonds shown
Skeletal Formula
The 2 dimensional arrangement of atoms in compound, showing all atoms except Carbon and Hydrogen, and all bonds except C-H
Structural Formula
1 dimensional representation of how atoms are arranged in a compound
Ideal Gas Equation
pV=nRT
p=pressure in pascals (Pa)
V=volume in cubic meters (m^3)
n=number of moles (mol)
R=gas constant, 8.31 (J/mol/K)
T=temperature in Kelvin (K)
K=C+273
3 - Bonding
Covalent Bond
A shared pair of electrons
Between uncharged atoms of similar electronegativity (+/- <0.2)

Electrons are shared an equal distance between atoms
Ionic/Electrovalent Bond
Polar Bond
When an electron is donated from one atom to another
This creates 2 oppositely charged ions which experience strong electromagnetic attraction
Dative Covalent Bond / Co-ordinate Bond
A covalent bond in which both electrons come from the same atom
Represented by an arrow from the electron donor to the reciever
N
H
H
H
H
A covalent bond in which electrons are shared unequally. They are pulled closer to the atom with greatest electronegativity
Polar Molecule
Contains polar bonds, and therefore partially charged atoms

Are usually more reactive

Can be solvents and are soluble
4 - Periodicity
Periodic Table
A table containing information on all 188 known elements
Has their: name, symbol, atomic number, relative atomic mass and category

Published by Dmitri Mendeleev in 1869
Period
Row of the periodic table, in which all atoms have similar mass and the same number of shells – equivalent to period number
Group
Column of the periodic table, in which all atoms have similar chemical properties and same number electrons in outermost shell – equivalent to group number
Across Period 3: Atomic Radius
Decreases:
-Larger effective nuclear charge - greater pull on electrons
-Same shielding
Across Period 3: 1st Ionization Energy
Na to Mg:
Increases
- greater nuclear charge
Mg to Al:
Decreases
- outer electron in higher energy 3p orbital
Al to P:
Increases
- greater nuclear charge
P to S:
Decreases
- outer electron experiences mutual repulsion
S to Ar:
Increases
- greater nuclear charge
5 - Organic Chemistry
Hydrocarbon
Compound containing only Hydrogen and Carbon atoms
Alkane
Saturated hydrocarbon

No double bonds

General formula CnH2n+2
Alkene
Unsaturated hydrocarbon

Contains double bonds

General formula CnH2n
Cyclo Alkane
Cyclic Molecule
Molecule that contains a ring structure
Cyclobutane
Octane
Saturated hydrocarbon

No double bonds

General formula CnH2n
Prop-1-ene
Naming Alkanes
Based on number of C atoms
Suffix is always 'ane'
1-methane
2-ethane
3-propane
4-butane
5-pentane
6-hexane
7-heptane
8-octane
9-nonane
10-decane
11-Undecane
12-Dodecane
20-Icosane
50-Pentacontane
100-Hectane
Naming Alkenes
Chain length is named same as alkanes

Suffix is always 'ene'

Number is always placed in middle of name to indicate the position of the double bond. Eg. pent-2-ene
Named the same as corresponding alkanes +cyclo
Homologous Series
Group of chemicals which have same functional group but differ in chain length by CH2

They have similar chemical properties but different physical properties
Isomerism
Isomers –
Molecules that contain the same atoms, but are arranged differently
Structural Isomers
Molecules that have the same molecular formula but different structural formula
Geometric Isomerism
Chain Isomerism
Has the same molecular formula, but different chain length (due to branching)
Has the same molecular formula, but functional groups are at different positions along the chain
Position Isomer
Eg. C3H7OH
Propan-1-ol Vs
Propan-2-ol
Eg. C4H10
Butane Vs methylpropane
Functional Group Isomer
Has the same molecular formula, but a different functional group. This greatly affects chemical properties.
Eg.C4H8
But-1-ene Vs
Cyclobutane
6 - Alkanes
Intermolecular
Forces
Van Der Waals/
Temporary dipole
Electrons repel
Temporary partial charges attract
Happens between molecules without polar bonds - all atoms have similar electronegativity

eg. Diatomic
Molecules
Forces between molecules
Are broken when the chemical melts or boils
Dipole-Dipole
Happens between partially charged atoms
Stronger than VDWs
Weaker than hydrogen bonding
H
Cl
H
Cl
Strong covalent bond
Weak intermolecular attractive force
Hydrogen Bonding
Same as dipole-dipole but only between atoms with greatest difference in electronegativity
2.20
3.04
3.44
3.98
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