Atomic Structure and the Periodic Table

Define an atom

The smallest parts of an element that can exist

Define an element

Substances containing only 1 type of atom

Define a compound

Substances containing two or more different types of atoms, chemically bonded

Radius of an atom

$$1\cdot10^{-10}$$

Radius of an atom

$1\cdot10^{-10}$m

Radius of nucleus

$1\cdot10^{-14}$ m

Where is most of the mass of an atom concentrated in?

The nucleus

Electron relative mass and charge

Mass: negligible

Charge: -1

Proton relative mass and charge

Mass: 1

Charge: +1

Neutron relative mass and charge

Mass: 1

Charge: no charge/0

Why are atoms neutral?

Have the same number of protons as electrons, charge on electrons is same size as change on protons, but opposite, so cancel out

What is the atomic number?

How many protons there are

What is the mass number?

Total number of protons and neutrons

What are isotopes?

Atoms of the same element, have the same number of protons but a different number of neutrons

How to calculate relative atomic mass?

[Sum of (isotope abundance x isotope mass number) ] divided by (sum of abundances of all isotopes)

Chromatography required practical

• draw a pencil line near the bottom of chromatography paper

• put a spot of (colour) ink on the pencil line

• place the paper in beaker of solvent with the spot above solvent level

• solvent rises and dyes separate

• if any dyes in ink are insoluble in solvent used, will stay on baseline

• when solvent has nearly reached top of paper, take paper out of beaker to dry

• end result is pattern of spots called chromatogram

What is the mobile and stationary phase of chromatography?

Mobile: solvent

Stationary: chromatography paper

What does filtration do?

Removes large, insoluble particles from a liquid

Evaporation practical

• pour solution into evaporating dish

• slowly heat solution, solvent will evaporate and solution will get more concentrated

• eventually, crystals will start to form, keep heating evaporating dish until dry crystals are left

Crystallisation practical

• pour solution into evaporating dish

• gently heat to speed up rate of reaction and to partially evaporate water

• then leave solution to crystallise using water bath, pat dry using filter paper

Simple distillation practical

• used for separating out a liquid from a solution

• solution is heated, part with lowest boiling point evaporates first

• vapour is cooled, condenses and collected in beaker

• rest of solution is left behind in flask

What was atomic theory, whose theory?

the idea that everything is made up from tiny particles that can’t be broken down any further, separated from each other by empty space. Democritus

John Dalton

• 19th century

• described the atom as solid spheres

• suggested different types of spheres make up different elements

J.J.Thomson

• 1897

• plum pudding model

• experiments proved atoms couldn’t be solid spheres, must contain - charge particles

• proposed that atoms are balls of positive charge, electrons embedded in it

• discovered electron

Ernest Rutherford

• 1909

• fired + alpha particles at + gold foil, some alpha passed through, some deflected to sides, some deflected backwards, prove Thomson wrong

• nuclear model: nucleus containing positive charge, negative charge existed as a cloud around nucleus

Neils Bohr

• 1913

• electrons orbit nucleus on shells

• orbiting of the atom is what prevents atom from collapsing (significant)

• many experiments support

What did Rutherford discover in further experiments?

Protons, nucleus made of particles

James Chadwick

• 1932

• provided evidence for neutral particles in nucleus: neutrons

Johann Dobereiner

• triads

• noticed elements with similar chemical properties occurred in threes

John Newlands

• arranged elements in order of increasing atomic weight

• saw every eighth element reacts in a similar way, called this his law of octaves

What was the problem with Newlands’ law of octaves?

Sometimes elements were grouped together when they had totally different properties when in order of atomic weight

Dmitri Mendeleev

• first modern periodic table

• started by arranging elements in order of increasing atomic weight

• if he needed to, would switch order of elements so fit patterns of other elements in same group

• left gaps for elements that hadn’t been discovered

• predicted properties of undiscovered elements, based on other elements in same groups

What was later discovered about the elements Mendeleev predicted?

When the missing elements were discovered, their properties matched his predictions, so scientists accepted his table was correct

Modern periodic table

Elements arranged in order of atomic number, number of protons, so every element in correct group

Problem with Mendeleev’s periodic table

Ordered by atomic weight, so elements can appear in wrong order due to presence of isotopes, group 0 not fully discovered when he made his table

Basic physical properties of metals

• strong (hard to break), but can be bent, hammered into different shapes (malleable)

• good conductors of electricity and heat

• high melting and boiling points

Basic physical properties of non-metals

• dull

• brittle

• aren’t always solid at room temp

• don’t generally conduct electricity

• often have lower density than metals

Properties of transition metals

• good conductors of heat and electricity

• very dense, strong, shiny

• can have more than one ion (e.g. Cu+ and Cu+2)

• often coloured

• often make good catalysts

• high melting, boiling point

Group 1 metals

• soft, can be cut, tarnish when cut (oxidise)

• shiny, low density

• trends going down group: increasing reactivity, lower melting and boiling points, higher relative atomic mass

Why does reactivity increase going down group 1?

• going down group, size of atom increases

• so increase in number of electron shells, radius of atom increases

• so greater distance between nucleus and outer electron, so electron less attracted to nucleus

• outer electron repelled by electrons in internal energy levels, called shielding

• decreases attraction between nucleus and outer electron, becomes easier to lose outer electron ,so reactivity increases down group

Group 1 metals reaction with oxygen

• react rapidly

• tarnish, oxidation

Group 1 reaction with chlorine

• react vigorously when heated in chlorine gas

• forms white crystalline salts, soluble in water

• chlorine changes colour

Lithium reaction with water

• lithium reacts rapidly with water

• effervescence / fizzing

• UVI turns purple → alkaline solution

• floats

Sodium reaction with water

• gas being produced

• UVI turns purple

• moves across solution, reacts more rapidly than lithium

Potassium reaction with water

• gas is produced

• UVI turns purple

• very rapid

• dashes across surface

Compare group 1 metals to transition metals

• group 1 metals more reactive than transition, react more vigorously with water, oxygen, group 7 elements

• group 1 metals much less dense, strong, hard than transition metals

• group 1 metals have much lower boiling points

What are group 7 elements known as?

Halogens

Describe fluorine at room temp

Very reactive, poisonous pale yellow gas

describe chlorine at room temp

fairly reactive, poisonous, dense pale green gas

Describe bromine at room temp

Dense, poisonous, red-brown volatile liquid

Describe iodine at room temp

Dark grey crystalline solid or a purple vapour

What kind of molecules do halogens exist as?

diatomic molecules, made of two atoms chemically bonded together

what are the trends going down group 7?

• become less reactive

• have higher melting and boiling points

• have higher relative atomic masses

why does reactivity decrease going down group 7?

• going down group, size of atom increases

• so increase in number of electron shells, radius of atom increases

• so greater distance between nucleus and outer electron, so electron less attracted to nucleus

• outer electron repelled by electrons in internal energy levels, called shielding

• decreases attraction between nucleus and outer electron, becomes harder to gain an electron, so reactivity decreases down group

why does melting and boiling point decrease going down group 7?

• molecules become larger

• so intermolecular forces between molecules becomes stronger

• so more energy is required to overcome these forces

what are group 0 elements called?

noble gases

what do noble gases exist as? (diatomic or monatomic)

monatomic, single atoms not bonded to each other

at room temperature, what colour are elements in group 0?

all colourless

as noble gases are inert, what does that mean?

they are non-flammable

why are noble gases unreactive?

they all have a full outer shell, eight electrons on outer shell, apart from helium, has two

what happens to boiling point and relative atomic mass going down group 0?

increases

why does boiling point increase as you go down group 0?

• increase in number of electrons in each atom

• so greater intermolecular forces

• so more energy required to overcome forces