14 — Periodic table Flashcards
Groups
Vertical column of elements
18 groups
Elements in same group hv same number of valence electrons and thus hv similar chemical properties
Periods
Horizontal row of elements
7 periods
Number of electron shells an element has is the same as its period number
Metalloids
Contain properties of both metals and non-metals
Trends across the period
Across the period, there is a decrease in metallic property and an increase in non-metallic properties -> increasing tendency to gain e-
Explain why the metallic property of elements across the period decreases
The number of protons in the nucleus increases while number of electron shells remain the same. The increase in nuclear charge results in a stronger forces of attraction between the nucleus and valence electrons. More energy is needed to lose electrons, resulting in lower tendency for the atom to lose electrons. Thus, the metallic property decreases.
Why there is an increase in metallic properties and decrease in non-metallic properties down the group
Down the group, the size of the atom increases due to an increase in the number of electron shells. The valence electrons r further away from the nucleus. Hence, there is weaker forces of attraction between the nucleus and the valence electrons. There is a higher tendency for the atom to lose its valence electrons to form a positive ion.
Group 1 properties
Elements in group 1 — alkali metals. They react w water to form soluble metal hydroxides.
Physical properties of alkali metals:
1. Soft and can be cut easily
2. Good conductors of heat and electricity due to presence of delocalised mobile electrons
3. Low melting and boiling points
4. Low densities
Group 1 physical properties trend
Down the group, the melting and boiling points of alkali metals decreases. Size of atom down the group increases due to increase in number of electron shells, the valence electrons r further away from the positive nucleus, hence the forces of attraction between the nucleus and valence electrons r weaker. Metallic bonding is weaker and less energy is needed to overcome the forces of attraction.
Furthermore, the density of alkali metals generally increases.
Chemical properties of group 1 elements
- They have 1 valence electron and react by losing 1 valence electron to achieve noble gas electronic configuration
- Reducing power of alkali metals increases down the group (powerful reducing agents)
- Reactivity increases down the group
Size of atom increases due to increase in number of valence electron shells. The valence electrons are further away from the nucleus hence there are weaker forces of attraction betw the nucleus and the valence electrons. There is an increase in the ease of losing valence electrons. - They react with water to form alkali and hydrogen gas
Order of reactivity: Li<Na<K<Rb<Cs<Fr
Group 1 elements and their reaction w water
- Lithium -> reacts quickly. Lithium floats on water
2Li(s) + 2H2O (l) -> 2LiOH (aq) + H2 (g) - Sodium -> reacts violently. Sodium darts around the water surface. Reaction may be explosive.
2Na(s) + 2H2O (l) -> 2NaOH (aq) + H2 (g) - Potassium -> reacts very violently. Reaction is explosive.
2K(s) + 2H2O (l) -> 2KOH (at) + H2 (g)
Physical properties of halogen
- Group 17 elements
- Exist as diatomic molecules
- Are non-metals
- Have low melting and boiling points
- Are coloured
Appearance of halogen at rtp
Fluorine -> pale yellow gas
Chlorine -> yellow-green gas
Bromine -> red-brown liquid
Iodine -> purple-black solid
Astatine -> black solid
Trend in physical properties down group 17 and explanation
- Down the group, melting and boiling point increases.
Size of molecule increases, resulting in stronger intermolecular forces of attraction. Thus more energy is needed to overcome the stronger forces of attraction.
2.colour intensity increases
(Covalent bonds in diatomic molecule stronger as size increases)
Chemical properties of halogens
- Reactive non-metals -> have 7 valence electrons -> have a tendency to gain 1 e- to achieve noble gas electronic configuration
- Oxidising power of halogens decrease down the group (Oxidising agents)
- React w most metals to form salts called halides (eg fluoride bromide)
- Reactivity of halogens decreases down the group as size of atom increases due to increase in number of electron shells. Forces of attraction betw the +ve nucleus and the valence e- r weaker, making it harder for the nucleus to attract 1 more electron.
Order of reactivity: F2>Cl2>Br2>I2>At2>Ts2
Displacement of halogens
The more reactive the halogen, the higher tendency it has to gain electrons to form negative ions compared to a less reactive halogen. Thus a more reactive halogen will displace a less reactive halogen from its halide solution.