Writing electronic structures, how the periodic table is arranged, why Mendeleev left gaps, and the difference between metals and non-metals.
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1.How many electrons fit in the first shell?
Two.
2.How many electrons fit in the second and third shells?
Eight in each, at this level of study.
3.Which shell fills first?
The one closest to the nucleus, because it is at the lowest energy level.
4.Write the electronic structure of sodium, atomic number 11.
2,8,1
5.Write the electronic structure of oxygen, atomic number 8.
2,6
6.Write the electronic structure of calcium, atomic number 20.
2,8,8,2
7.How is the periodic table arranged?
In order of increasing atomic number, with elements arranged so that those with similar properties fall into columns.
8.What is a group and what does it tell you?
A vertical column. All elements in a group have the same number of electrons in their outer shell, which is why they react similarly.
9.What is a period and what does it tell you?
A horizontal row. The period number tells you how many occupied electron shells the atoms have.
10.How can you tell the number of outer electrons from the periodic table?
It is the group number, for groups 1 to 7. Group 0 elements have full outer shells.
11.How did Newlands arrange the elements?
In order of atomic weight, in rows of seven, noticing that similar elements appeared at regular intervals.
12.Why was the work of Newlands not accepted?
He forced elements into groups where they did not fit, left no gaps for undiscovered elements, and sometimes put very different elements together.
13.How did Mendeleev improve on this?
He also ordered by atomic weight, but left gaps for elements not yet discovered and changed the order of some elements where the properties demanded it.
14.Why was leaving gaps so important?
The properties of the missing elements could be predicted, and when they were discovered they matched the predictions, which convinced people the table was correct.
15.Why did some elements appear out of atomic weight order?
Because of isotopes, which change the average atomic weight. Once the table was ordered by atomic number rather than weight, the problem disappeared.
16.What did the discovery of the structure of the atom confirm?
That ordering by atomic number was correct, and that groups share properties because they share the same outer electron arrangement.
17.Where are metals found in the periodic table?
On the left and towards the bottom.
18.Where are non-metals found?
Towards the right and the top.
19.What do metal atoms tend to do in reactions?
Lose electrons from their outer shell to form positive ions.
20.What do non-metal atoms tend to do in reactions?
Gain or share electrons to fill their outer shell, often forming negative ions.
21.Give four typical physical properties of metals.
Good conductors of heat and electricity, shiny when cut, malleable, and generally high melting points.
22.Give three typical physical properties of non-metals.
Poor conductors of heat and electricity, dull, and brittle when solid.
23.Why do elements in the same group react in similar ways?
They have the same number of electrons in their outer shell, and it is the outer electrons that determine chemical behaviour.
24.Why are the noble gases unreactive?
They have a full outer shell of electrons, so they have no tendency to gain, lose or share electrons.
25.What happens to the number of shells going down a group?
It increases by one for each period, so the atoms get larger.
26.Why does atomic size matter for reactivity?
The further the outer electrons are from the nucleus, the weaker the attraction holding them, which makes them easier to lose and harder to gain.
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