Higher Chemistry - Unit 1 - Chemical changes and structure

Covalent radius

a measure of the size of an atom, half the distance between nuclei of two covalently bonded atoms of an element

covalent radius along period

nuclear charge increases, number of filled shells remains same.

covalent radius down group

number of filled shells increases, nuclear charge increases.

screening / shielding meaning

"shields" outer electrons from positive nucleus so outer electrons are less strongly attracted to the nucleus

ionisation energy

energy required to remove one mole of electrons from one mole of gaseous atoms

first ionisation energy

energy required to remove one mole of electrons from one mole of atoms in the gaseous state

what is the first ionisation energy equation of magnesium

Mg(g)----Mg+ (g) + e-

what happens to ionisation energy across a period

nuclear charge increasing, ionisation energy increase along each period

what happens to the ionisation energy down a group

less energy required to remove an electron, ionisation energy decreases

What does an increase in nuclear charge cause?

the outer electrons to be more strongly attracted to the nucleus

what does an increase in number of electron shells cause?

outer electrons to be screened/shielded from the nucleus

Electronegativity

a measure of the attraction an atom involved in a bond has for the electrons of the bond.

trend in electronegativity

higher the value of element, the stronger its attraction for electrons

what happens to the electronegativity along a period

nuclear charge increases so, increase in electronegativity

what happens to the electronegativity down a group

electrons are less strongly attracted to atoms so decrease in electronegativity

what is pure covalent bonding

occurs in compounds where both atoms have same electronegativity value, as both atoms have equal pull on shared electron

examples of pure covalent bonding

between diatomic elements

what is a polar covalent bond

\- when one atom with a higher electronegativity attracts electron more strongly than the other atom

* Delta positive (δ+) and delta negative (δ-) notation used to indicate partial charges on atoms, which give rise to a dipole.

what is ionic bonding

• atoms with large difference in electronegativity, inolves the transferring of electrons from one atom to another.

• electrostatic attraction between positive and negative ions

ionic compounds are held togther in the solid state by ______ ______

ionic bonds

covalent network compounds are held together in the solid state by _________ ______

covalent bonds

covalent molecules are held together in the solid state by forces of attraction know as ____ ___ _____ _______

van der waals' forces

What are the three types of Van der Waals forces?

London Dispersion Forces, Hydrogen Bonding,Permanent Dipole Permanent dipole

hydrogen bonding is the ___________ of the three intermolecular attractions

strongest

Due to the stronger attractions, hydrogen bonded compounds have much _______ melting and boiling points

higher

what is the general rule for solubility

like dissolves like \n (i.e., polar dissolves polar \n non-polar dissolves non-polar)

pure covalent vs ionic

\- considered opposites on the bonding continumm, with polar covalent lying inbetween

what are van der Waals forces

Intermolecular forces between moleules \n - LDF'S \n - PDP-PDP that include hydrogen bonding

What are London Dispersion Forces

forces of attraction that can operate between all atoms and molecules

• weakest bonds

• formed as a result of electrostatic attraction between temporary dipoles and induced dipoles

When does london dispersion forces occur?

between all molecules + atoms but only force between NON-POLAR molecules and MONATOMIC elements.

What is an induced dipole

when neighbouring atom shifts from approaching delta negative causing delta positive to appear

What causes LDF'S?

caused by uneven distribution of moving electrons. \n forms temporary dipoles with slightly positive and negative sides.

when do permanent dipole-permanent dipole interactions occur

between polar molecules

When is a molecule polar?

- If it has a permanent dipole

What is a Permanent dipole-Permanent dipole

* additional electrostatic forces of attraction between polar molecules
* stronger than LDF'S
* permanent dipole of one molecule attracted to a neighbouring one

what are hydrogen bonds

* Electrostatic forces of attraction that contain highly polar bonds directly between F, O, N.
* stronger than PDP-PPD but weaker than covalent

How to determine strength of intermolecular forces?

- melting points - boiling points- viscosity

What does hydrogen bonding affect?

- boiling points \n - melting points \n - viscosity/miscibility

What element's boling points are affected by hydrogen bonds?

ammonia - water - hydrogen fluoride

Reduction and Oxidation

OIL \n oxidation is loss \n RIG \n reduction is gain

What is a viscous liquid

Liquid that has strong intermolecular forces between molecules.

what does increasing the number of hydroxyl groups in a molecule do?

\- increases viscosity \n - increases mp & bp

molecules with stronger intermolecular forces will have higher melting and boiling points and a ________ ____________

higher viscosity

oxidising agent meaning

substance that accepts electrons

* (an oxidising agent is something that causes another substance to be oxidised and is reduced in the process)
* group 7 strongest oxidising agents

reducing agent meaning

substance that donates electrons

• -(a reducing agent is something that causes another substance to be reduced and is oxidised in the process).

• group 1 strongest reducing agents

How to tell if its a reducing agent

\- elements with low electronegativities tend to lose electrons, act as reducing agents

How to tell if its an oxidising agent

elements with high electronegativities tend to gain electrons, act as oxidising agents

Uses of oxidising agents

\- kills fungi and bacteria \n - breaks down coloured compounds, makes ideal for use as 'bleach'

Strongest oxidising agents

\- bottom left-hand column of electrochemical series \n F2(g)

Strongest reducing agents

\- top right-hand column of electrochemical series \n Li(s)

rate of reaction formula

what are the intermolecular forces between pure covalent molecular elements?

weak London dispersion forces (LDF)

What is metallic bonding

the electrostatic attraction between the positive ions and the delocalised electrons, these delocalised electrons allow them to conduct electricity

when do successful collisions occur

- collision geometry is correct \n - particles have energy equal to or greater than the activation energy

activation energy

the minimum amount of kinetic energy needed for a reaction to occur

how does temperature effect the rate of reaction

temprature increases

energy distribution graphs are used for

are used to show the energies of the particles

what does the shaded part of the energy distribution graph mean

all the molecules in that area have energy greater than the activation energy

what happens in an exothermic reaction

heat energy been released to surrundings

ΔH has a negative value as energy has been lost.

what happens in an endothermic reaction

products have more energy than reactants due to energy being taken in from surroundings

how do catalysts effect rate of reaction

• speed up chemical reactions without being used up

• lowers activation energy, allowing more reactions to occur

Activated complex meaning

The activated complex has the highest chemical potential energy in the reaction pathway (always higher than either the products or reactants), because it is an unstable arrangement of the atoms