Chemistry: Atomic bonding and structure

What holds and atom together?

Electrostatic forces

What are isotopes?

An element that has the same number of protons but a different number of neutrons which results in a different atomic mass

What physical properties change with isotopes?

Nuclear stability and mass

How do you get radioactive decay?

When electrostatic repulsion is greater than nuclear force

What is the relative atomic mass?

The ratio of weighted average mass per atom of the naturally occurring form of the element to 1/12 the mass of an atom

What is an allotrope?

The same element with different structure

In the periodic table, which way does atomic radius increase and decrease?

Decreases across a period because the electrons are closer to the nucleus

Increases down a group because there are more energy level results

What is ionisation energy?

The amount of energy needed to remove an electron from a neutral atom when it is a gas

What is electronegativity

The ability of an atom to form bonds with an electron

Noble gases have no electronegativity because they have full shells

In the periodic table, which way does electronegativity increase and decrease?

Increases across a period because the nucleus is more positive so attracts electrons more

Decreases down a group because there are more energy levels so attraction between electrons and the nucleus is less

What is electron affinity?

The ability of an atom in the gas state to accept an electron and form a negative ion

←→+ Up and down -

What is metallic character?

Describes the set of properties associated with metals

Across +. Up and down -

Depends upon the ability to lose valence electrons

What is the elemental spectra?

When all the electrons are at the lowest levels, an atom is at ground state

What is an excited state?

When electrons gain energy to move to a higher energy state

What is absorption?

When an electron is in a excited state and moves to a higher energy level it absorbs incoming photons

What is emission?

When and electron drops back to its energy level it emits photons in the form of light

What does the light emitted or absorbed directly correlate to?

The distance the electron has moved between shells

What is an absorption spectrum?

A line spectra that shows what happens when an atom absorbs certain frequencies of light that is absorbed

What is an emission spectrum?

A line spectra that shows frequencies that are emitted

What is emission spectroscopy used to identify?

Elements based upon their unique set of energy levels

Elements will emit light with a unique set of wavelengths

The pattern for one element is always the same

Why are line spectra’s important?

• They can help determine the composition of stars

• They allow us to determine the relative amount of carbon dioxide in the atmosphere

• They allow us to determine the concentrations of different elements in a solution

What does atomic absorption spectroscopy rely on?

It relies on electron transfer between atomic energy levels and can be used to determine metallic elements

What is atomic absorption spectroscopy determine?

The concentration of different elements in solution

How is the analysis of atomic absorption spectroscopy performed?

This technique involves focusing light of a specific wavelength on atoms of a solution and measuring the amount of light that is absorbed

How does atomic absorption spectroscopy work?

• For the instrument to work it requires:

  • a flame as a heat source

  • A method of spraying the sample solution into the flame

  • A beam of light for the atom to absorb

  • A way to focus and detect light

  • A device to show the calibration graph and to calculate results

• The light from the hollow cathode lamp is focused through the flame

• The atoms in the flame absorb the light

• That which is not absorbed is focused by a monochromatic or and measured by a detector

• The amount of transmitted light is used to calculate the amount of absorbed light

What does mass spectrometry determine?

The mass and relative abundance of each isotope

How does mass spectrometry work?

• Vaporisation-needs a vaporised sample

• Ionisation-the sample is ionised by the high energy electron beam

• Acceleration-the ions are accelerated to have the same kinetic energy

• Deflection-a magnet field deflects the ions based on their mass. Lighter ions are deflected more

• Detection-the ions are passed through a mass analyser and detected based on their mass to charge (m/z) ratio

What are pure substances?

Materials with distinct measurable properties (melting point, boiling point, reactivity, strength, density)

What are mixtures?

Materials that have material properties dependent on the identity and relative amounts of the substances that make up the mixture

What are heterogeneous material?

They have two or more different substances and their proportions can vary

Mixtures are non uniform

What is a homogeneous material?

A uniform composition

The pure substances are elements and compounds

They are a solution( the only mixture that can be homegeneous

What are physical and chemical properties of pure substances?

• Has distinct measurable properties

• Can be used to identify substances

What are physical and chemical properties of mixtures?

• The properties depend on both the identity and relative amounts of substances that make up the mixture

• The properties of the components in a mixture determines the technique used to separate them

What are some physical properties?

• Melting point

• Boiling point

• Electrical conductivity

• Thermal conductivity

• Strength

• Density

• Solubility

• State

• Ductility

• Mallibility

What are some chemical properties?

• Decomposition by heat

• Effect of light

• Reactions with

  • water

  • Acids

  • Bases

  • Oxygen

  • Etc

What can chemical change be recognised as?

• Precipitate is formed

• Gas produced

• Colour change

• Significant change in temperature

• An insoluble liquid disappears

• Separation by differences in particle

• Separation by differences in boiling point

• Separation by density and solubility

• Separation by magnetism and electrostatic attraction

What is an ionic bond?

It is a bond between positive cations and negative anions are attracted. They form an electrostatic bond (non metal and metal bond)

What does polar mean?

One end is more positive than the other end

What is a covalent molecular substance?

Is composed of discrete molecules (low melting point, soft, usually liquid or gases)

What is a covalent network substance?

A 3D network (hard, very high melting points, solids)

When does multiple covalent bonding occur?

When atoms share more than one pair of electrons a multiple covalent bond will form eg O=O

What are properties of covalent network substances?

• High melting points because the covalent bond is strong

• Non conductors of electricity because there are no charged particles that are free to move throughout the structure

• Hard and brittle because the bonds are strong between atoms so it’s difficult to scratch but an impact force disrupts the position of the atoms and causes the network to shatter

• Insoluble in water because there is no attraction between the atoms in the network and water molecules

What are allotropes of carbon?

• Diamond

• Graphite

• Fullerenes

What are properties of diamond?

• 3D network

• High melting point

• Non conductors of electricity

• Insoluble

• Unreactive

What are properties of graphite?

• High melting point

• Good electricity conductor

• Insoluble

• Soft

What are properties of fullerenes?

• Soft

• Slippery

• Non conductors of electricity

• Insoluble in water

• Typically low melting points

• Not a covalent network substance

What is nanotechnology?

The study of extremely small substances often called nanoparticles

How big is a nanometre?

1×10^-9m

What uses does nanotechnology have in health?

• Sunscreen-zinc oxide/ titanium oxide is used to stop up rays

• Bandages-silver nanocrystals are used to stop bacteria growth

What are properties of polar covalent molecular substances?

• Low melting point

• Low boiling point

• Poor electrical conductivity

What is the chemical reactivity of alkanes?

• Unreactive

• Combustion- Will burn in oxygen to produce water, carbon dioxide and heat

• Substitution- May be replaced with a chlorine or bromine if sufficient energy is present

What are the chemical reactivity of alkenes?

• Presence of double bond makes them reactive

• Combustion C4H8+6O2 → 4CO2+4H2O

• Reaction with hydrogen CH2=CH2+H2 → CH3CH3

• Reaction with halogen

• Reaction with water

• Polymerisation-long chains can form polymers

• When a symmetrical reagent eg H2 is added to the product of the reaction has the same group attached to each carbon

• When an asymmetrical reagent eg water is added to an asymmetrical alkene there are two possible products generally H will go to the carbon with greater number of hydrogens

What is the chemical formula of benzene?

C6H6