atomic structure and bonding

history of atoms, periodic table, trends in pt, mass spectrometry, atomic absorption spectrometry, isotopes, pure substances, mixtures, separation techniques, ionic bonding, metallic bonding, % composition

Who made and what are 5 atomic structure discoveries that have lead to current understanding of atoms?

1. John Dalton - current understanding of atom

2. J.J. Thomson - electron discovery

3. Ernest Rutherford - discovery of nucleus and proton

4. James Chadwick - understanding of neutron

5. Neils Bohr - that electrons move in fixed energy levels

What did John Dalton discover (5)

elements are made of atoms

atoms are identical in physical and chemical properties

mass cannot be created or destroyed

chemical reactions are the rearrangement of atoms

compounds form from combinations of atoms in simple specific ratios

what did jj thomson discover

mass of electron is 9.11 × 10^-31

the (shortlived) plum pudding model to illustrate arrangement of particles

emission of stream of particles and coloured light when electricity passes through cathode ray tube(electrons)

what did ernest rutherford find out

by firing alpha particles at gold sheet, he observed deflection patterns where some passed and some deflected

conclude that atom is mostly empty space with + charge in middle

firing alpha particles into N gas, discover proton due to presence of hydrogen

what did james chadwick discover

by firing alpha particles into Be, discovered the neutron

postulated that neutral particles existed in atom

what did neils bohr discover

suggested that the orbits correspond to specific energy states and e^- can jump between levels through absorption and emission

who are 6 people that contributed to the construction of periodic table? and how

1. antoine lavoisier: categorised into gas, non metal, metal and earths

2. johann dobereiner: identified groups of 3 elements with similar properties as ‘triads’

3. Alexandre B. de Chancourtis: created ‘telluric screw’ which displays based on atomic weight

4. john newlands: created ‘law of octaves’ where similar property elements appear every 8 elements

5. julius L. meyer: arrangement by atomic weight, grouped by valency

6. dmitri mendeleev: first widely recognised pt. organised by increasing atomic weight with some gaps of unknown elements

alkali metals

highly reactive

1 valence eal

alkali earth metals

reactive

2 valence e

transition metals

less reactive than alkali

ion formation produces colour

rare earth metals

e.g actinides, lanthanides

highly reactive

radioactive isotopes

complex e- structure

all metals are silvery true or false

false alkali and alkali earth metals are only silvery

halogens (nm)

highly reactive

7 valence e

noble gas (nm)

not reactive

8 valence e

gas at room temp

metalloids (nm)

m and nm properties

others (nm) (6)

C, N, O, P, S, Se

4-6 valence e

what are elements, how can they exist

substances made of only one type of atom

as large networks called diamonds, small molecules or solitary atoms

what can H be used for

reacts with O in fuel cells to produce electricity for vehicles

what can Ne be used for

its gas form is collected in tube and electric current passes to ionise atoms producing light

what can W be used for

using tungsten filament, withstand high temperatures as it has high melting point, in halogen light bulb

what is first ionisation energy? what does it mean if its small/large ionisation energy?

the quantity of energy needed to remove the first electron from an atom

small ion. energy means the elements prefers to lose e- (it has fewer e)

large ion energy means element prefers to gain e- (it has many e)

Why does first ion. energy increase when moving across period?

-there are more protons

-will naturally increase the attraction on e-

-therefore more energy required to remove e

why does first ion, energy decrease when moving down a group?

-there are more energy levels

-valence e are further from nucleus and not held as tight

-less energy is required to remove e

what is electronegativity? what does it mean to have low/high electronegativity?

the tendency to attract e-

low: atoms wants to lose e rather than gain, metals have large radius

high: atoms need few e to fill. non metals have small radius

why does electronegativity increase when moving across? how is it further reinforced?

-the higher + charge attracts more strongly

therefore easier to attract e

shielding effect remains same

effective nuclear charge felt by outer e increase

enhancing E.N.

why does electronegativity decrease when moving down? how is it enhanced?

-due to the increase in e shell

-e are further, the attraction is weakened

harder to attract more e

shielding effect reduces effective nuclear charge and E.N. decrease because the more shells, the further outer shells are repelled

what are the trends in metallic character

decreases from left to right, up (F)

increases from right to left, bottom (Francium)

why does atomic radius increase when moving down group

additional e shells

valence e pushed further out

there a larger radius

why does atomic radius decrease when moving across a period

there are more protons

increase e attraction between protons and e

pulling shells inward

decreasing size of atom radius

define ionisation

the process by which atom gains or loses e to be an ion

define desolvation

the process of removing solvent molecules from solute particle’s surface

what does light move as and why

moves through space as transverse waves

because it is part of electromagnetic spectrum

the electromagnetic spectrum consists of

wavelength - distance of one wave (m)

amplitude - distance a wave moves from rest (m)

frequency - # of waves occuring per sec (Hz)

how is bohr’s discovery relevant to absorption and emission?

discovery: e- orbit in fixed energy levels at a fixed distance from nucleus

1. absorption: of wavelengths of light causes e- to enter ‘excited’ state, they jump from lower energy level to higher energy levels

2. emission: when they are in excited state and the energy is removed, e transition back to lower level to gain stability, emitting photon

-the higher the wave frequency of energy, the greater the transition

describe the absorption spectra

dark lines correspond to the wavelengths absorbed by gas showing different light that can be absorbed

describe the emission spectra

coloured lines correspond to wavelengths of electromagnetic radiation emitted during transition

what is atomic absorption spectroscopy

focusing light of a specific wavelength on atoms of a solution to measure the amount of light absorption it takes in

Different elements can be in a solution to detect one specific element true or false

false

list the process of a basic atomic absorption spectrometer (7)

1. solution is drawn through a thin tube and the nebuliser turns it into a fine aerosol

2. the fine spray is mixed with air and acetylene in spray chamber

3. it is pushed towards burner and ignited

4. spray undergoes desolvation and atoms are released into flame

5. the hollow cathode lamp provides thin steady beam of light of a wavelength specific to the element

6. light is transmitted through the flame

7. light is focused in the monochromator into the photomultiplier tube where the electrical signals turned into absorbance value

what are isotopes? how do they differ from normal atoms and why?

an atom of an element that has the same number of protons but different number of neutrons

they have same chemical properties as e are only involved in chem react.

but different physical properties because different atomic mass

what is mass spectrometry? how is it calculated

ions are detected and sorted based on their mass:charge ratio

mass:charge = atomic mass/charge of cation

Environmental analysis is an example of ________________. It detects ___________ in the environment to __________ and __________ it.

application of mass spectrometry

contaminants

monitor

protect

an exmaple of application of mass spectrometry is ___________ ___________. It analyses ______ or ______.

clinical diagnostics

blood

urine

Food quality can be analysed in ______ __________. It detects _________ in food to ensure _______ and ______

mass spectrometry

additives

safety

quality

list the process of mass spectrometry(4)

1. ionisation: atoms are turned into cations by removing the e when heated by ionisation source

2. acceleration: ions are accelerated towards the magnetic field by negatively charge disc

3. deflection: they are deflected by magnetic field to the detected based on mass:charge ratio

4. detection: ions of each isotope reach detector to determine abundance

what is relative atomic mass? what does it indicate

a quantity that compares the average mass of an element’s atoms to one-twelfth of carbon-12’s mass

indicate how many times heavier it is compared to C-12

relative atomic mass formula

the sum of isotopic abundance multiply by isotopic mass divided by 100

what is a pure substance

matter with fixed composition and unique properties such as oxygen

% abundance formula

peak height divided by total height multiply by 100

if an element is a pure substance can it be broken down?

no because it consists of one type of atom

e.g. gold, silver, nitrogen

if a compound is a pure substance can it be broken down?

yes because compounds are 2 or more elements chemically combined

through filtration, distillation or evaporation

what is a mixture

matter containing at least two physically combined compounds

describe a homogenous mixture and give an example

uniform composition through meaning different components are evenly distributed and cannot be easily distinguished

saltwater

descirbe a heterogenous mixture and give an example

non uniform composition meaning different components can be seen and separated. individual properties retain their properties

oil and water

what are ten physical separation techniques

1. filtration

2. separation by particle size

3. separation by density

4. evaporation

5. crystillisation

6. distillation

7. fractional distillation

8. electrostatic separation

9. chromatography

10. magnetic separation

what is filtration, what does it use to separate

separation of insoluble substances from soluble substances

the porous barrier separates solid and liquid leaving solid in filter paper

sieving - by particle size

separate different solids with particle size

gravitational filtration - particle size

rely on weight of solid particles to filter

vacuum filtration - by particle size

useful is particles are light and you want mixture to be dried out

sedimentation - by density

denser material falls to the bottom allowing decantation of liquid at the top

separation funnel - by density

when liquids don’t mix, funnel has tap to let densest material at the bottom out

centrifugation - by density

use centrifuge to settle finer particles

evaporation is ______. describe the four steps of evaporation (4)

separation and purification of a substance

1. preparing: dissolved substance placed in evaporation dish

2. heating: e.g. bunsen burner, water bath

3. concentration: solution becomes more concentrated with the dissolved substance

4. completion: heat until residue left behind

crystallisation,

formation of pure solid substance from dissolved substance solution

as substance evaporations, dissolved substances collects as a crystal

distillation, describe steps for it (5), give one example

separation based on difference in boiling points of a solution’s components

1. heat: the lowest b.p. component vaporised first

2. vaporise: it travels through distillation column

3. condensation: reaches the condenser where cooled by water and condensed back into a liquid

4. collection : distillatecollected in separate container

5. residue: remaining mixture processed further/discards

e.g. alcoholic beverage production

fractional distillation, describe the steps and give an example

separate mixtures of liquids with different boiling points

1. heating: lowest b.p. component vapourise first

2. fractionating column: enter f.c. which has large surface area allowing repeated condensation + vaporisation

3. condensation + vaporisation: when it rises thru f.c. it cools and condenses. the heat from vapour causes continual vaporisation of condensed liquid improving component separation

4. collection: distillate collected in separate container

5. fractional collection: different components collected at different temperatures each separated based on boiling point

6. residue: processed further/discarded

chemical purification

electrostatic separation, describe steps 4 and give an example

separate based on their electrical charge

1. charging: particles given electrical charge by passing electrical field

2. feeding: fed on conveyor belt which is opposite charge to attract particles

3. separation: different charged particles attracted to different areas of belt

4. collection: in different bins

fine particles

chromatography and example

relies on stickiness of a material to static medium

paper chromatography

magnetic separation, describe steps

based on magnetic properties

1. feeding: onto conveyor belt/magnetic separator

2. magnetic field: belt passes magnetic field which is generated by electro magnet

3. attraction: magnetic particles attracted and adhere to surface, non magnetic particles not affected by m, field + continue along the belt

4. separation: magnetic particles carried away from non magnetic particles

5. collection: in diff bins

material with different magnetic properties

what is % composition? how do you calculate it

the % by mass of each element/component

% composition = # atoms of element x atomic mass divided by sum of atomic masses for the compound x 100

what is the formula for % composition for mixtures

mass of component divded by mass of mixture x 100

what is ionic bonding

the transfer of e between a metal which donates and non metal which accepts

what are 3 examples of uses of ionic compounds

1. toothpaste - NaFl used for dental hygiene

2. food - NaCl to improve taste

3. pool chemicals - sodium hypochlorite to produce chlorine in pools

what four properties of ions

1. can conduct electricity in liquid state only

2. high melting + boiling points

3. hard & brittle

4. varying solubility

Explain why ions can conduct electricity in liquid state

1. when solid, particles in fixed positions and are immobile

2. this prevents electrical charge transfer through particles

3. while in liquid state, particles are free to move through the medium

4. this allows the transfer of electrical charge

explain why ions have high melting and boiling points

1. large amounts of energy are needed to disrupt the strong electrostatic forces of attraction

2. therefore higher temperatures are needed for this to occur

explain why ions are hard and brittle

1. the ionic lattice structure is an alternation of cation and anions

2. when force is applied, interactions of similar charge particles occur

3. this causes repulsion causing ion to shatter/splinter

explain why ions vary in solubility

1. when dissolved in water, ionic bonds dissociate and form new bonds with H₂O molecules

the size and charge of ion affect their solubility

substances with high lattice energy (the energy that holds cations and anions together in a compound) are less likely to be soluble

ammonium

caesium

copper(I)

Cu⁺

hydrogen

H⁺

silver

Ag⁺

rubidium

Rb⁺

copper(II)

Cu²⁺

cobalt(II)

Co²⁺

iron(II)

Fe²⁺

lead(II)

Pb²⁺

manganese(II)

Mn²⁺

strontium

Sr²⁺

zinc

Zn²⁺

chromium(III)

Cr³⁺

iron(III)

Fe³⁺

bromide

Br^-

chloride

Cl^-

cyanide

CN^-

dihydrogenphosphate

ethanoate (acetate)

CH₃COO^-

fluoride

F^-

hydrogencarbonate