- 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
What are the atomic and mass numbers?
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
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
What is inside an atom?
Proton - mass = 1, charge = +1
Neutron - mass = 1, charge = 0
Electron - mass = very small (0), charge = -1
- middle of the atom
- contains protons and neutrons
- radius of 1 x 10^-14m
- positive charge
- move around in shells
- negatively charged
- volume = atom size
- no mass
How do you calculate relative atomic mass?
sum of (isotope abundance x isotope mass number) / sum of abundance of all the isotopes
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
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)
Chemical reactions shown in equations
- methane + oxygen -> carbon dioxide + water
Symbol equations (must be balanced)
- 2Mg + O2 -> 2MgO
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
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
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
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
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
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
Alpha particle scattering experiment
- 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
Bohr's nuclear model
- suggested that the electrons orbit in shells
- each shell is at a fixed distance from the nucleus
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
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
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
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
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
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
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