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Atomic Atomic Structure and Structure and
Electron Electron ArrangementArrangement
UNIT 2Aim A
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Columns of elements
What are columns of elements called?
groups1 2 43 5 6 07
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Rows of elements
periodsWhat are rows of elements called?
1
2
3
4
5
6
7
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Groups and periods
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What is the structure of an atom?
Protons, neutrons and electrons are not evenly distributed in an atom.
The electrons are spread out around the edge of the atom. They orbit the nucleus in layers called shells.
The protons and neutrons exist in a dense core at the centre of the atom. This is called the nucleus.
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What is the atomic number?
What are the atomic numbers of these elements?
11
26
50
9
tin
iron
sodium
fluorine
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How are electrons arranged?
Electrons are not evenly spread but exist in layers called shells. (The shells can also be called energy levels).
The arrangement of electrons in these shells is often called the electron configuration..
Note that this diagram is not drawn to scale – the atom is mostly empty space. If the electron shells were the size shown, the nucleus would be too small to see.
1st shell
2nd shell
3rd shell
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How many electrons per shell?
Each shell has a maximum number of electrons that it can hold. Electrons will fill the shells nearest the nucleus first.
1st shell holdsa maximum of2 electrons
2nd shell holdsa maximum of8 electrons
3rd shell holdsa maximum of8 electrons
This electron arrangement is written as 2,8,8.
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What is the atomic number?
Every element has a unique atomic number. This is the number of protons in the nucleus of each atom.
What is the atomic number of this helium atom?
A neutral atom must have equal numbers of protons and electrons, so the atomic number of an element also gives the number of electrons.
Helium has 2 protons, so its atomic number is 2.
Atoms are neutrally charged, so what links atomic number and the number of electrons?
electron
proton
neutron
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Summary: the atom so far
The nucleus is:
made up of protons and neutrons
positively charged because of the protons
dense – it contains nearly all the mass of the atom in a tiny space.
Electrons are:
very small and light, and negatively charged
able to be lost or gained in chemical reactions
found thinly spread around the outside of the nucleus, orbiting in layers called shells.
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Calculate electron configurations
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What are the properties of elements?
A property is any characteristic feature of a substance.
Properties of sodium include:
The chemical properties of an element are determined by its atomic number.
Are there any patterns in the properties of the elements?
highly reactive
solid but melts easily
feels light (low density).
Can you name any properties of the element sodium?
A property is any characteristic feature of a substance.
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Metals to non-metals, solids to gases
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Patterns: reactivity of metals
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po
Rb Sr Y Zr NbMo Tc Ru Rh Pd Ag Cd In Sn
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga
Na Mg Al
Li Be
What happens to the reactivity of metals down a group?
Which is the most reactive metal?
increase in reactivity
incr
ease
in
rea
ctiv
ity
What happens to the reactivity of metals along a period?
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Which metal is more reactive?
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Patterns: reactivity of non-metals
increase in reactivity
Group 0 elements are the most unreactive of all elements.
For the remaining non-metals and semi-metals, reactivity increases up a group and along a period from left to right.
Which is the most reactive non-metal/semi-metal?
At Rn
Sb Te I Xe
Ge As Se Br Kr
Si P S Cl Ar
B C N O F Ne
He
incr
ease
in
rea
ctiv
ity
unreactive
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What are the patterns of electron arrangement?
Consider the electron arrangements of the first 20 elements in the periodic table.
What is the pattern of outer shell electrons in a group?
2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8
1 2 43 5 6 07
1
2
3
4
2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8
1 2
2,8,8,1 2,8,8,2
What is the pattern of outer shell electrons across a period?
What is the pattern of full electron shells in a group?
