Chemistry- Atomic Structure

What does the particulate nature of matter state?

all substances are made of tiny, invisible particles

Atom definition

the smallest particle of an element that still has the properties of that element

What does Dalton’s assume?

all matter is made of tiny particles and the particles are indivisible

What did J.J. Thompson discover?

The electron

How were electrons discovered?

cathode rays were passed through a hole in a positive electrode, when no charge between two plates, rays went straight, when positive charge in the top plate, rays when up therefore negatively charged

Cathode definiton

negative electrode, conductor of electricity

What is the value of the charge of the electron?

1.6 × 10^-19 coulomb

Features of the plum pudding model

-sphere of positive charge

-electrons randomly embedded

Who developed the first nuclear model of the atom?

Ernest Rutherford

what are alpha particles

positively charged particles produced by certain radioactive substances

what are alpha particles made of?

two groups of two neutrons and two protons stuck together

Rutherford’s experiment explained

thin sheet of gold foil bombarded with alpha particles, phosphorescent screen used to detect the particles through light flashes in a microscope, the positive nucleus repels the positive particles

Results of Rutherford’s experiment

-most particles passed undeflected

-some particles deflected at large angles (close to nucleus)

-some bounced back on their path (direct hit)

Size of the nucleus

1/100,000 size of an atom

How were protons discovered?

different substances bombarded with alpha particles, lighter atoms gave off small, positive particles that didn’t happen with heavy particles, the alpha particles broke up the nuclei of the atom

Assumptions of the first nuclear model of the atom

• atoms have a small, dense, positive core with most of mass

• nucleus has protons

• atom is mostly empty space

• electrons scattered in space around nucleus and moving

Limitations of the first nuclear model of the atom

• why dosent the nucleus fly apart because of protons repelling each other?

• why dont the electrons fly into the nucleus?

How were neutrons discovered?

James Chadwick bombarded beryllium with alpha particles, produced a radiation of no charge that could knock protons from paraffin wax, named neutrons

Charge of protons

+1

Charge of neutrons

0

Charge of electrons

-1

Mass of protons

1

Mass of neutrons

1

Mass of electrons

1/1838

Spectrum definition

white light passes through glass prism, broken into separate colours

What device measures the spectrum?

spectrometer

What colour is sodium’s flame?

yellow

What colour is strontium’s flame?

red

What colour is barium’s flame?

green

What colour potassium’s is flame?

lilac

What colour is copper’s flame?

blue-green

What is quantisation of electron energy?

the idea that electrons have a fixed amount of energy, introduced by Bohr

Assumptions of Bohr’s model

-electrons are in orbits around the nucleus and have fixed energy

-the energy of each electron in the levels are fixed

-electrons in orbit dont gain or lose energy

What are the three light series called?

Lynman, Balmer and Paschen series

What does Heinsenber’s uncertainty principal state?

it is impossible to measure both the velocity and position of an electron at the same time

Limitations of Bohr’s model

-failed to account for multiple lines on the LES

-didn’t account for wave motion of electrons

-claimed certainty of electron velocity and position

-didn’t account for sublevels

Orbital defintion

a region of space within which there is a high possibility of finding an electron

What shape is the s level?

spherical, differ in size

What shape is the p level?

dumb-bell shaped, three parts (X Y Z)

What is a sublevel?

a division of the main energy level with one or more orbitals of same energy

Assumptions of Rutherford’s Nuclear Model

• atoms have dense, positive core called nucleus

• most of mass in nucleus

• most of atom is empty space

• electrons scattered in electron cloud surrounding nucleus

Limitations of Rutherford’s nuclear model

• if like charges repel, why dosen’t nucleus repel itself?

• if opposite charges attract, why dont electrons spiral into nucleus?

Atomic number

number of protons in the nucleus of an atom

Mass number

Sum of the number of protons and neutrons in the nucleus of an atom

Relative atomic mass

• average of the mass numbers of the isotopes of an element

• as they occur naturally

• taking abundances into account

• expressed on scale where carbon-12 isotope have mass of exactly 12 units

Isotopes definition

atoms of the same element with different mass numbers due to different numbers of neutrons in the nucleus

What is group 1 called on the periodic table

alkali metal

What is group two called on periodic table

alkaline- earth metals

What is the 17th group in the periodic table

Halogens

What is the 18th group in the periodic table

Noble gases

Group 1 element properties

• very soft

• low densities

• similar properties

• very reactive

Why do all group 1 atoms have similar propreties

electronic structure of their atoms- all have one electron in outer shell

What happens to reactivity of Group 1 elements as you go down the group

increases

Why does the reactivity of period increase as you go down a group

• atoms get larger

• outer electron further from the nucleus

• attraction between nucleus and outer electron weakens

Group 2 element properties

• strong redcing agents

• good conductors

• higher melting and boiling point

• reactive

• oxides are basic, and form colourless salts

Group 17 element properties

• react to produce salts

• highly reactive

• reactivity decreases down group

Group 18 element propreties

• very unreactive

• low boiling points

• useful for when non-reactive gas needed

Differences between Medleev’s and modern periodic table

• arranged in increasing mass/increasing atomic number

• contains gaps/ no gaps

• only 60 elements/ over 100 elements

• transitions not in separate block/ in separate block

What LES is this

sodium

What LES is this

strontium

What LES is this

copper

What is quantitisation of energy

the idea that an electron can only have a fixed amount of energy (a quantum of energy)

Assumptions of Bohr’s theory

• electrons revolve around the nucleus in fixed paths called orbits

• electrons in an orbit have a fixed amount of energy

• energy levels are represented by the letter n

• energy of an electron in a particular orbit is quantitised

• electrons in one particular energy level neither gains nor loses energy

• atoms normally exist in ground state to occupy lowest available energy levels

• electrons in ground state have energy of fixed values

• giving energy to atoms in ground state means specific amount is absorbed and electrons jump to excited state

• energy absorbed is equal to the difference in energy between the lower and excited state

• electrons in excited state are unstable and will fall back down

• electrons release photons of light energy when falling down

• energy of a photon is definite and fixed

• frequency of light emitted depends on difference in energy levels (E2-E1 = hf)

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