Chemistry unit 1

Atom

the smallest part of an element that can exist

Compounds are formed from…

Elements by chemical reactions

Chemical reactions always involve…

The formation of one or more new substances

Chemical reactions often involve…

A detectable energy change

Compounds contain…

Two or more elements chemically combined in fixed proportions

Compounds can only be separated into elements by…

Chemical reactions

A mixture consists of…

Two or more elements or compounds not chemically combined together

The chemical properties of each substance in the mixture are…

Unchanged

Mixtures can be separated by…

Physical processes

The 5 physical processes

Filtration

Crystallisation

Simple distillation

Fractional distillation

Chromatography

Physical processes do not involve… and no new…

Do not involve chemical reactions and no new substances are made

Filtration

Crystallisation

Simple distillation

Fractional distillation

Filtration method

Filtration is used to separate an insoluble solid from a liquid.

Involves a circle of filter paper folded to make a cone and placed into a filter funnel.

The filtrate is the liquid which passes through the filter paper and the residue is the solid left on the filter paper.

Crystallisation method

Is used to produce solid crystals from a solution.

1. A solution is placed in an evaporating basin and heated with a Bunsen burner.

2. The volume of the solution decreases because some of the water has evaporated. Solid particles begin to form in the basin.

3. After the remaining solution has cooled down, filter the excess liquid and leave the crystals to dry.

Simple distillation method:

Is used to separate a solvent from a solution. Simple distillation works because the dissolved solute has a much higher boiling point that the solvent.

When the solution is heated solvent vapour evaporates from the solution. The gas moves away and is cooled and condensed. The remaining solution becomes more concentrated in solute as the amount of solvent in it decreases,

Fractional distillation method:

Is used to separate different liquids from a mixture of liquids.

It works because the different liquids have different boiling points.

1. When the mixture is heated vapours rise through a column which is hot at the bottom and cold at the top.

2. Vapours condense when they reach a part of the column that is below the temperature of their boiling point.

3. The liquid flows out of the column.

Paper chromatography:

Is used to separate mixtures of soluble substances. Food colouring, ink, dye

Solvent

The liquid in which the solute dissolves to form a solution

Solution

Mixture formed by a solute and a solvent

Solute

The dissolved substance in a solution

Development of the atom

First → tiny spheres

Then discovery of the electron → led to plum pudding model

Next alpha particle scattering experiment → led to the nuclear model

Finally → Bohr suggested that electrons orbit the nucleus at specific distances

Then → Chadwick discovered neutrons

First model of the atom

Atoms were thought to be tiny spheres that could not be divided

Plum pudding model

The atom is a ball of positive charge with negative electrons embedded in it.

Alpha particle scattering experiment

Led to the conclusion that atoms are mainly empty space and the mass is concentrated at the nucleus, which is charged.

Nuclear model

Mostly empty space and the mass of the atom is concentrated at the nucleus which is charged,

Bohr’s adaptation

Suggested that the electrons orbit the nucleus at specific distances.

Later experiment led to the idea that…

The positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. These particles were given the name proton.

James Chadwick’s experimental work

Provided the evidence to show the existence of neutrons within the nucleus.

This was about 20 years after the nucleus became an accepted scientific idea.

Relative electrical charge

Proton: +1

Neutron: 0

Electron: -1

In an atom, the number of electrons is equal to the number of…

Protons in the nucleus

Do atoms have an overall electrical charge?

Atoms have no overall electrical charge.

Atomic number =

Number of protons

All atoms of a particular element have the same number of…

Protons

Atoms are very small having a radius of about…

0.1nm (1 × 10 ^ -10 m)

The radius of a nucleus is less than about

1/10 000 of that of the atom

Almost all of the mass of an atom is in…

The nucleus

Relative masses

Proton: 1

Neutron: 1

Electron: very small

The sun of the protons and neutrons in an atom is its…

Mass number

Atoms of the same element can have different numbers of…

Neutrons

Atoms of the same element with a different number of neutrons are called…

Isotopes of that element

Relative atomic mass calculation:

(mass x %) + (mass x %)

---

100

Electronic structure:

The electrons in an atom occupy…

The lowest available energy levels.

Period

→

Group

^

How many electrons can fit on each shell

2, 8, 8

Elements with a full outer shell go in Group…

0

Ions are…

Atoms which have an overall charge (because they have lost or gained electrons)

Positive ions have … electrons

Lost electrons

Negative ions have … electrons

Gained electrons

The elements in the periodic table are arranged in order of

Atomic (proton) number

Due to elements being arranged in order of atomic number…

Elements with similar properties are in the same group.

It is called the periodic table because…

Similar properties occur at regular intervals.

Elements in the same group have…

The same number of electrons in their outer shell (this gives them similar chemical properties)

Before protons, neutrons and electrons were discovered; scientists arranged the elements in order of…

Their atomic weights

The early periodic tables were incomplete and some elements were placed in inappropriate groups if…

The strict order of atomic weights was followed

Mendeleev overcame some of the problems by…

Leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights

Elements with properties predicted by Mendeleev were discovered and filled the gap…

Isotopes made it possible to explain why the order based on atomic weight was not always correct.

Elements that react to form positive ions are…

Metals

Elements that do not form positive ions are…

Non-metals

The majority of elements are…

Metals

On the periodic table metals are..

Bottom left

On the periodic table non-metals are…

Top right

Elements in group 0 are called…

Noble gases

Noble gases are…

1. Unreactive

2. Do not easily form molecules because their atoms have stable arrangements of electrons.

Noble gases have … electrons in their outer shell

8

EXCEPT helium which only has…

2

What happens to the boiling points of noble gases with increasing relative atomic mass (going down the group)

Increase

The elements in group 1 are called…

Alkali metals

Alkali metals have characteristic properties because…

Of the single electron in their outer shell

In group 1, the reactivity of the elements … going down the group

Increases

Reaction of lithium and water

Reacts vigorously to produce hydrogen and lithium hydroxide

Reaction of sodium and water

1. React vigorously to produce hydrogen and sodium hydroxide

Reaction of potassium and water

1. Burns violently with sparks and a lilac flame

2. Produces hydrogen and potassium hydroxide

Reaction of lithium and oxygen

1. Burns with a strongly red tinged flame

2. Producing a white sold called lithium oxide

Reaction of sodium and oxygen

1. Burns with a strong orange flame

2. Produce a white solid, sodium oxide

Reaction of potassium and oxygen

1. Burns vigorously with a lilac flame

Produces a white solid, potassium oxide

Reaction of lithium and chlorine

1. React rapidly to produce white lithium chloride

Reaction of sodium and chlorine

1. Reacts rapidly to form white sodium chloride

Reaction of potassium and chlorine

1. Reacts rapidly to produce white potassium chloride

Group 7 elements are called…

Halogens

Halogens have similar reactions because…

They all have seven electron in their outer shell

Halogens are non-metals and…

Consist of molecules made of pairs of atoms

Halogens react with metals to form…

Ionic compound in which the halide carries a -1 charge

Halogens react with non-metals to form

Covalent compounds where there is shared pair of electrons

In group 7, the further down the group, the higher its…

1. Relative molecular mass (the size of the molecule)

2. Melting point

3. Boiling point

In group 7, the reactivity… going down the group

Decreases

Reactivity decrease going down the group because…

1. Halogens react by gaining an electron to achieve a full outer shell (when they act like this their name ends in -ide)

2. As you go down, the number of shells increases, the element attracts electrons from other atoms less, so doesn’t react as easily

Conclusion: increased distance + increased shielding

Decrease in reactivity means…

A more reactive halogen (one higher up the group) can displace a less reactive halogen from an aqueous solution of its salt.

Why do group 1 elements increase in reactivity going down the group?

1. As we move down Group 1, the distance between the positive nucleus and negative outer electron increases.

2. As this distance increases, the outer electron is less attracted to the positive nucleus.

3. Also, the outer electron is shielded. Which also decreases the attraction between the nucleus and outer electron,

Transition elements

Metals with similar properties, which are different from those of the group 1 elements.

Properties of group 1 metals:

Soft

Relatively low melting points

Low density

React rapidly with oxygen, chlorine and water

When they react they form ions with 1+ charge

Properties of transition metals:

Harder and stronger

Have higher melting points

Have higher densities

Much less reactive: react slowly with oxygen and chlorine

Form ions with different charges

Form coloured compounds

Act as catalysts

Why are elements not instantly widely accepted?

Time is needed for peer review