Topic 12 Flashcards
What order are elements arranged in the periodic table?
Elements are arranged in the order of atomic number (NOT relative atomic mass) in the Periodic Table.
What is periodicity?
The repeating pattern of physical and chemical properties as shown by the different periods is known as periodicity.
What is special about elements in the same group of the periodic table?
Elements in the same group tend to have similar chemical and physical properties.
All Group I metals react with O2 to form ____ metal oxides.
basic
Arrange sodium, aluminium, silicon and sulphur in decreasing order of electrical conductivity at room conditions, and explain your answer in terms of bonding and structure. (5 marks) [DSE 2016]
Note: 1 mark is for communication.
- Electrical conductivity: aluminium > sodium > silicon > sulphur (or: silicon = sulphur) [1 M)
Any 3 of the following items, each 1 mark [3 M]
- Both aluminium and sodium have giant metallic structures with delocalised / mobile electrons so that electrical conductivity of them is high / their electrical conductivity is higher than that of silicon and sulphur. (1 M)
- The number of delocalised / mobile electrons of aluminium is more than that of sodium so that electrical conductivity of aluminium is higher than that of sodium. (1 M)
- Silicon has giant covalent structure and its electrons are not mobile and cannot conduct electricity / its electrical conductivity is lower than that of aluminium and sodium. (1 M)
OR Silicon has giant covalent structure and its electrons are not mobile. But silicon is a semi-metal and can conduct electricity in some conditions. (1 M)
- Sulphur has simple molecular structure and its electrons are not mobile and cannot conduct electricity / its electrical conductivity is lower than that of aluminium and sodium. (1 M)
Communication mark:
Chemical knowledge = 0 to 2, communication mark = 0
Chemical knowledge = 3 to 4, communication mark = 0 or 1
Name 2 semi-metals.
Boron, Silicon
State the physical states of all elements in the periodic table at 25°C and 1 atm.
Liquid:
- Br (l)
- Hg (l)
Gas: (6 noble gases)
- H2 (g)
- N2 (g)
- O2 (g)
- F2 (g)
- Cl2 (g)
Solid:
- all others
What is the trend of atomic radius in a periodic table?
Atomic radius decreases from left to right and increases down a group
State the 3 steps to compare the atomic sizes/radii of different atoms/ions:
Strictly follow the steps below to compare the atomic sizes / radii of different atoms / ions:
1. Compare the number of occupied e shells: larger number of occupied e shells = larger in atomic size/radius (e.g. Cl > F)
2. Compare the number of p+: smaller number of p+ = larger in atomic size/radius (e.g. O > F)
3. Compare the number of e-: larger number of e- = larger in atomic size/radius (e.g. Fe2+ > Fe3+)
What is the general trend of atomic size in the periodic table?
The closer to the noble gases, the smaller the atomic size
Define electronegativity.
Electronegativity is defined as the ability of an atom to attract e- in a chemical bond.
What is the trend of electronegativity in the periodic table?
Electronegativity increases from left to right across the periodic table and decreases down a group
Why do noble gases not have electronegativity values? (And which is the exception?)
Noble gases don’t form bonds
(Exception: Xe)
Why does graphite have delocalized electrons but diamond does not?
Diamond and graphite C atoms both have 4 outermost shell electrons. In diamond, all 4 electrons are used to form bonds so it has no delocalized electrons. In graphite, only 3 of the electrons are used to form bonds, hence there is one delocalized electron per atom.
