# Chemsitry C1

• Created by: abbiedye
• Created on: 29-06-18 21:53

## What are elements?

- 100 different elements

- Elements are substances that contain atoms with the same number of protons

- all the atoms of a particular element have the same number of protons

- different elements have atoms with different numbers of protons

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## What do the atomic and mass numbers show?

- Atoms - neutral (same number of protons and electrons)

- Ion - protons don't equal electrons (2- charge ions - two more electrons than protons)

- Atomic number = how many protons

- Mass number = total protons and neutrons

neutrons = mass number - atomic number

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## What are isotopes?

- same atomic number, different mass number

- Isotopes are different forms of the same element, which have the same number of protons but a different number of neutrons

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## What is inside an atom?

Proton - mass = 1, charge = +1

Neutron - mass = 1, charge = 0

Electron - mass = very small (0), charge = -1

Nucleus

• middle of the atom
• contains protons and neutrons
• radius of 1 x 10^-14m
• positive charge

Electrons

• move around in shells
• negatively charged
• volume = atom size
• no mass
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## How do you calculate relative atomic mass?

sum of (isotope abundance x isotope mass number) / sum of abundance of all the isotopes

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## What are compounds?

- When elements react, atoms combine with other atoms to form compounds

- Formed when two or more elements

• metal atoms - lose electrons and form positive ions
• non-metal atoms - gain electrons and form negative ions

- Properties are usually completely different from the orginal elements properties

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## How are compounds represented by formulas?

- Formulas are made up of elemental symbols in the same proportions found in the compound

carbon + oxygen -> carbon dioxide

C + O O -> OCO (CO2)

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## Chemical reactions shown in equations

Chemical equations

• methane + oxygen -> carbon dioxide + water

Symbol equations (must be balanced)

• 2Mg + O2 -> 2MgO
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## How can mixtures be separated?

- no chemical bonds in mixtures

- mixtures include air (mixture of gases) and crude oil (mixture of hydrocarbons)

- properties = properties of the separate parts

- chromatography is the process of separating different dyes in an ink and the pattern created by it is called a chromatogram

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## What are the different separation techniques?

- Filtration = insoluble liquid from a liquid reaction mixture (purification)

- Evaporation = (if salt doesn't decompose) soluble solids from solutions (dissolved) (heating until dry crystals)

- Crystallisation = heat in evaporating dish - until crystals form - filter - dry

EXAMPLE - Rock salt - dissolve in water - filter (sand not through) - evaporate - crystals

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## What is simple distillation

- it is used to separate out solutions

- the solution is heated and the lowest boiling point evaporates first

- the vapour cools, condenses and then is collected

- it can be used to separate pure water from sea water because they have very different boiling points

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## What is fractional distillation?

- used to separate a mixture of liquids

- heat with a fractionating column

- different liquids have different yet similar boiling points and evaporate at different temperatures

- lowest boiling points first and then raise the temperature after each liquid condenses

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## What is the history of the atom?

- John Dalton (19th century) - solid spheres

- JJ Thompson (1897) - weren't solid spheres (plum pudding)

- Ernest Rutherford (1909) - alpha particle scattering (concentrated positive mass - nucleus - mostly empty space - electrons)

- Niels Bohr - nuclear model - electron shells - orbit - helped to explain scientist's observations

- Rutherford - nucleus can be divided further - protons

- James Chadwick - neutrons in nucleus - close to modern day nuclear model

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## Plum pudding model of the atom

• Scientists used to think that atoms were solid spheres
• They then found atoms contain even smaller negatively charged particles - electrons
• The plum pudding model showed the atom as a ball of positive charge with electrons scattered
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## Alpha particle scattering experiment

Showed:

• tiny positively charged nucleus at the centre
• nucleus surrounded by negative electrons
• most of the mass is in the nucleus
• most of the atom is empty space
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## Bohr's nuclear model

- suggested that the electrons orbit in shells

- each shell is at a fixed distance from the nucleus

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## Electron shell rules

• Electrons always move in shells
• The inner shells are filled up first
• 1st shell = 2 electrons, 2nd shell = 8 electrons and 3rd shell = 8 electrons
• Atoms are a lot more stable when they have full shells
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## Development of the periodic table

• In 1869, a scientist called Mendeleev took all of the known elements and arranged them into a table
• He ordered them mainly by their atomic mass and properties
• He left gaps and predicted the properties of the missing elements
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## The modern periodic table

• There are about 100 elements
• In the periodic table, the elements are laid out in order of increasing atomic number
• Metals are found to the left and non-metals are found to the right
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## Metals and non-metals

• Metals are elements which can form positive ions and non-metals don't
• Metals are found on the bottom and left of the periodic table and non-metals are found on the top and right
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## What are the group 1 elements?

• 1+ ions
• The group 1 elements are reactive, soft metals
• They all have 1 electron in their outer shell. This makes them very reactive. It also gives them similar properties
• As you go down the elements, reactivity increases and melting and boiling points get lower - higher atomic masses
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## What are the group 7 elements?

• 1- ions
• The Halogens are fluorine, chlorine, bromine, iodine, and astatine
• As elements, the halogens form molecules that contain two atoms. For example, chlorine (Cl2) is a fairly reactive, poisonous green gas
• As you go down group 7, the halogens become less reactive - higher atomic masses
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## What are the group 0 elements?

• Group 0 elements are called the noble gases. They include the elements helium, neon, and argon
• All elements in group 0 are colourless gases at room temperature
• They all have eight outer shell electrons, apart from helium which has two
• They are non-flammable
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