Element Guide. Atomic Number : number of protons which is equal to the number of electrons. 2. Element Symbol. He. 4. Atomic Mass Number = The number of protons + the number of neutrons. The Periodic Table.
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Atomic Number: number of protons which is equal to the number of electrons
Atomic Mass Number = The number of protons + the number of neutrons.
The columns in the periodic table are called groups. Groups of elements share similar reactivity.
This is because they have the same number of valence electrons.
Group 1 are the alkali metals
Group 7 Halogens
Group 8 Noble gases
The rows in the periodic table are called periods.
Atom’s size decreases from left to right in a given period
Group 1 metals are known as the ‘ alkali metals’
As you go DOWN Group 1, the alkali metals become more reactive - the valence (outermost) electron is more easily lost, because it’s further from the nucleus and more shielded from it by inner shells.
1) The alkali metals all have ONE valence (outer most) electron. This makes them very reactive and gives them all similar properties
2) They all have the following physical properties:
3) The alkali metals always form ionic compounds.
As you go DOWN Group 7, the halogens become LESS reactive - there’s less force to pull the extra electron in when it’s further away from the nucleusand more shielding electrons
Halogens react with alkali metals to form salts
2Na + Cl2 2NaCl
2K + Br2 2KBr
More reactive halogen will displace less reactive one
Cl2 + 2KI 2KCl + I2
Cl2 + 2KBr 2KCl + Br2
I2 + KCl No reaction
Br2 + 2KCl No reaction
These seven elements occur naturally as molecules containing two atoms.
The octet rulestates that atoms are most stable when they have a full shell of electrons in the outside electron ring.
All of the Group 1 elements have one electron in the outside shell and they all have a valence of plus one. Group 1 elements will lose one and only one electron, that single outside electron to become a single positive ion with a full electron shell of eight electrons (an octet)
Group 2 elements all have two electrons in the outer shell and all have a valence of plus two.
Group 3 elements have a valence of plus three. Boron is a bit of an exception to this because it is so small it tends to bond covalently.
Aluminium has a valence of +3, but some of the larger Group 3 elements have more than one valence.
Small Group 5 elements, nitrogen and phosphorus, are non-metals. They tend to either gain three electrons to make an octet or bond covalently. The larger Group 5 elements have more metallic character.
Group 7 elements all have seven electrons in the outer shell and either gain one electron to become a -1 ion or they make one covalent bond. The Group 7 elements are diatomic gases due to the strong tendency to bond to each other with a covalent bond.
Electrons are are arranged in shells around the nucleus. Each shell is a different energy level.
The first shell fits up to…
The second fits up to…
The third fits up to…
So the electron shell arrangement for 12Mg would be…
2, 8, 2
Interactive periodic table
Na Ca I O
____________ (such as NaCl) are generally formed between metals and nonmetals.
A CATION forms when an atom ______ one or more electrons.
An ANION forms when an atom ______ one or more electrons
F + e- --> ____
Mg ______--> Mg2+
State the number of protons, neutrons, and electrons in each of these ions.
39 K+16O -241Ca +2
19 8 20
#p+ ______ ______ _______
#no ______ ______ _______
#e- ______ ______ _______
Write the nuclear symbol form for the following atoms or ions:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 46 e- ___________
The ions that have been formed are now ________ to oppositely charged ions.
So Mg2+ will be attracted to Cl-. This forms an ionic compound.
Some ionic compounds are soluble others are insoluble.
Compounds which are insoluble form solids called precipitates.
So Mg2+ will be attracted to Cl-.
Because Mg is 2+ and Cl is only 1-, Mg will attract 2 Cl’s.
The compound formed will be ______.
The subscript shows that they are 2 Cl’s for each Mg.
If the starting ions were Cu2+ and S2-, the 2 ions have the same charge. So each Cu will only attract 1 S.
The compound formed will be ______.
There is never any charges on the final product - they balance out
The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound.
A. Element in Group XVII, Period 4
1) Br 2) Cl 3) Mn
B. Element in Group II, Period 3
1) beryllium 2) magnesium 3) boron