Chemistry As Year 1 - Aqa

Each pair of electrons around an atom will repel all other electron pairs

The pairs of electrons will therefore take up positions as far apart as possible to minimise repulsion

...a shared pair or a lone pair

The shape adopted by a simple molecule or ion is that which keeps repulsive forces to a minimum

If there are five pairs of electrons, the shape usually adopted is that of a trigonal bypyramid

octahedral structure

Angles of a regular tetrahedron are all 109.5 degrees but lone pairs affect these angles.

Strong nuclear force which is much stronger than electrostatic forces of attraction holding electrons and protons together in an atom.

The average mass of an atom of an element relative to one twelfth of the mass of an atom of carbon-12

Material made up of one type of an atom

Made up of two or more elements are chemically bonded together

Made up of two or more elements aren't chemically bonded

An element that has the same number of electrons and protons but a different number of neutrons

Mass of a single isotope of an element relative to one twelfth the mass of an atom of carbon-12

Mass of an ionic compound or ions relative to one twelfth the mass of an atom of carbon-12

Different isotopes of the same element react chemically in exactly the same way as they have the same electron configuration

Atoms of different isotopes of the same element varies in mass number because of different number of neutrons in their nuclei

It's the most useful instrument for the accurate determination of relative atomic masses.

A scale on which the mass of an atom of carbon-12 is defined as exactly 12

The mass of separate atoms (or molecules).

The substance(s) in the sample are converted to positive ions accelerated to high speeds (depending on their m/z) and arrive at a detector.

Vacuum - whole apparatus is kept under a high vacuum to prevent ions that are produced colliding with molecules from the air

Ionisation - Sample to be investigated is dissolved in a volatile solvent and forced through a fine hollow needle connected to positive terminal of high voltage supply.

Produces tiny positively charged droplets having lost electrons to the positive charge of the supply.

Solvent evaporates from droplets into vacuum and droplets get smaller until become single positively charged ion.

Acceleration - Positive ions attracted towards negatively charged plate and accelerate towards it. Lighter ions and more highly charged ions achieve higher speed

Ion drift - Ions pass through a hole in negatively charged plate, forming beam and travel along a tube, celled flight tube to a detector.

Detection - ions with same charge arrive at the detector, lighter ones are first and have higher velocities.

Flight times are recorded, positive ions pick up electron from the detector causing a flowing current.

Different isotopes that makes up an element. Detection of individual ions so different isotopes are detected separately have different masses.

5 and high resolution mass spectrometry

particles

cloud

negative charge

An electron fills a volume in space

Two electrons in the same orbital must have opposite signs

Electrons are usually represented by arrows pointing up or down showing different directions of spin

Atomic orbitals of lower energy are filled first - lower main level's filled first and in this level, sub-shells of lower energy's filled first.

Atomic orbitals of same energy fill singly before pairing starts. Electrons repel each other.

No atomic orbital can hold more than two electrons

Energy required to remove a mole of electrons from a mole of atoms in the gaseous state and is measured in kJ mol^-1

First electron needs least energy to remove it due to it being removed from a neutral atom.

Second electron needs more energy than the first being removed from +1 ion

etc.

Ionisation energies usually increases across a period because the nuclear charge increases and makes it more difficult to remove an electron

Shows a general decrease in the first ionisation energy because outer electrons in a main level gets further from nucleus in each case

Nuclear charge increases and it would be more difficult to remove an electron.

The actual positive charge felt by an electron in outer shell less than full nuclear charge because effect of inner electrons shielding nuclear charge

average mass of an atom of an element __________________________________________

1/12 mass of one atom of carbon-12

or

average mass of an atom of an elementx12/mass of one atom of carbon-12

Mass of a molecule compared to 1/12 the relative atomic mass of an atom of carbon-12

average mass of one moleculex12/mass of one atom of carbon-12

Number of atoms in 12g of carbon-12

6.022x10^23

Amount of substance contains 6.022*10^23 particles

...grams contains one mole of atoms

...in grams containing one mole of entities

...ions or electrons

number of moles (n) = mass/m (g) ÷ mass of 1 mole/M (g)

no. of moles/n ÷ volume/V (dm^3)

concentration/c (mol dm^-3) * volume/V (dm^3) ÷ 1000

When atoms bond together they share or transfer electrons achieving more stable electron arrangement - often a full outer main level of electrons.

Ionic

Covalent

Metallic

One, two or three

Lose their outer electrons

Occurs between metals and non-metals

Electrons transferred from metal atoms to non-metal aoms

Positive and negative ions formed

Sodium ion's positively charged (lost a -ve electron)

Chloride ion's negatively charged (gained a -ve electron)

Two ions attracted to each other and to other oppositely charged ions by electrostatic forces.

Electrostatic attraction between oppositely charged ions.

Attraction extends throughout the compound and every +ve ion attracts every -ve ion, vice versa.

lattice

Always solids at room temp.

Have giant structures

High melting temp. because to melt an ionic compound must be supplied breaking up lattice of ions

Molten/dissolved because ions carry current are free to move in the liquid state aren't free in the solid state

(Ionic Compounds)

Forms a lattice alternating positive and negative ions. A blow in the direction shown may move the ions and produces contact of ions with like charges

Bond forms between pair of non-metal atoms

Atoms share some of their outer electrons so each atom has a stable noble gas arrangement

Covalent bond's a shared pair of electrons

...electrostatic attraction between the nuclei and the shared electrons taking place within the molecule

Four electrons shared. E.g. two atoms in an oxygen molecule sharing two pairs of electrons so oxygen atoms have a double bond between them.

Due to strong covalent bonds between the atoms within molecules.

Weak attractions between molecules as they do not need much energy to move apart from each other.

The molecules are neutral overall and no charged particles carrying the current.

Atom accepts electron pair is an atom doesn't have a filled outer main level of electrons - atom's electron-deficient

Atom that donates electrons has a pair of electrons not being used in a bond (lone pair)

The power of an atom attracts the electron density in a covalent bond towards itself

Often used to describe the way the -ve charge is distributed in a molecule

Measure of electronegativity. 0 to 4, greater the number, more electronegative the atom

Nuclear charge

Distance between nucleus and outer shell electrons

Shielding of nuclear charge by electrons in inner shells

Smaller the atom, closer the nucleus is to the shared outer main level electrons and greaer its electronegativity

The larger the nuclear charge, the greater the electronegativity

Increases (atoms get smaller) and less shielding by electrons in inner shells

The electronegativity increases and the nuclear charge increases, number of inner main levels remain the same and atoms become smaller

Polarity's about the unequal sharing of electrons between atoms that are bonded covalently. Property of the bond.

Very electronegative atom with lone pair of electrons.

These will be attracted to the partially charged H atom in another molecule and forms the bond.

Oxygen, Nitrogen, Fluorine

Shows a gradual increase in boiling point because only forces acting between atoms are van der Waals forces

Increases with number of electrons present

Higher than the hydrides of other elements in their groups because hydrogen's present between molecules in each of these compounds

Stronger intermolecular forces of attraction making molecules more difficult to seperate.

They are weaker than covalent bonds and can break or make under conditions where covalent bonds are unaffected.

No part of a covalent bonds and lone pairs affect shape of the molecule.

Has four pairs of electrons and one groups of a lone pair

With four pairs of electrons around N atom, ammonia molecule has a shape tetrahedron. Has a triangular pyramid.

Angles of a regular tetrahedron all 109.5degrees but lone pairs affect the angles. The angles compress due to repulsion

repulsion increases

↓ bonding pair - bonding pair

↓ lone pair-bonding pair

↓ lone pair-lone pair

Arrangement: Regular

Evidence: Crystal shapes have straight edges. Solids have definite shapes

Spacing: close

Evidence: Solids are not easilt compressed

Movement: vibrating about a point

Evidence: diffusion is slow. Solids expand when heated

Arrangement: Random

Evidence: Liquid changes shape to fill bottom of its container

Spacing: Close

Evidence: Liquids aren't easily compressed

Movement: Rapid 'jostling'

Evidence: Diffusion is slow. Liquids evaporate

Arrangement: Random

Evidence: None direct but a gas will fill its container

It shows distribution of energies at given temperatures

A higher proportion of molecules will reach the activation energy

The enthalpy change when one mole of substance is completely burnt in oxygen under standard conditions, all reactants and products being in their standard states.

Contains the functional group C-X where X is a halogen (F, Cl, Br or I)

Haloarenes

Haloalkanes

A halogen is attached to an aliphatic skeleton - alkyl group

Halogen's attached directly to a benzene ring

Boiling points increase with mass. The greater the branching the lower the boiling point.

Haloalkanes are soluble in organic solvents but insoluble in water - they are not polar enough and do not exhibit hydrogen bonding.

Enthalpy change when one mole of substance is formed its constituent elements under standard conditions, all reactants and products being in their standard states

Enthalpy change when 1 mole of substance's completely burned in oxygen with all reactants and products

Energy is transferred between system and surroundings

The amount of heat energy taken in or given out during any change in a system provided the pressure is constant

Energy transferred when 1 mole of the compound formed from its elements under standard conditions (298K and 100kPa), reactants and products bringing their standard states

Energy is given out to surroundings

Enthalpy change is negative

Products have less than reactants

Energy taken in from the surroundings

Enthalpy change is positive

Products have more energy than reactants