1.1 periodicity Flashcards
What is the definition of a group in the periodic table?
- vertical columns within the table
- similar chemical properties resulting f
- common number of electrons in the outer shell
What is the definition of a period in the periodic table?
- row of elements arranged
- increasing atomic number
- increasing number of outer electrons
- metallic to non-metallic characteristics.
which of the first 20 elements contains metallic bonding?
- Li
- Be
- Na
- Mg
- Al
- K
- Ca
Which of the first 20 elements has covalent molecular bonding?
- H2
- N2
- O2
- F2
- Cl2
- P4
- S8
- fullerenes (carbon)
which of the first 20 elements have monatomic bonding?
noble gasses
Which of the first 20 elements have a covalent network structure?
- B
- C (diamond, graphite)
- Si
What is covalent radius?
- a measure of the size of an atom
- it is half the distance between the nuclei of two covalently bonded atoms of an element
What is ionisation energy?
the energy required to remove one mole of electrons from one mole of gaseous atoms
What is electronegativity?
a measure of the attraction an atom involved in a bond has for the electrons of the bond
What is the definition of metallic bonding?
positive metal ions surrounded by a sea of delocalised electrons
What created stronger metallic bonds?
the more electrons that are contributed to the delocalised sea of electrons the stronger the metallic bond
what are the intra and inter molecular forces between covalent molecules?
intramolecular - covalent
intermolecular - London dispersion forces
Explain the structure of carbon in the form of diamond
- covalent network structure
- each carbon atom is covalently bonded to four other carbon atoms
- in a tetrahedral arrangement
Explain the structure of carbon in the form of graphite
- each carbon atom forms 3 covalent bonds to neighbouring carbon atoms
- forming layers of hexagonal rings
- the fourth outer electron becomes delocalised between the layers allowing graphite to conduct electricity
- the layers in graphite are held together between weak London dispersion forces
Why do monatomic element have low melting points?
the atoms are held together by weak London dispersion forces
What are the two trends of covalent radius?
- going across a period, covalent radius decreases
2. going down a group, covalent radius increases
Explain the trend of covalent radius going across a period
- going across a period the nuclear charge increases
- the number of energy levels remains the same
- an increase on nuclear charge results in the electrons being more strongly attracted to the nucleus, decreasing covalent radius
explain the trend of covalent radius going down group
- number of filled electron shells increases
- nuclear charge increases too
- the effect of increasing nuclear charge is outweighed by adding energy levels of electrons
- inner electrons shields the outer electrons from the positive nucleus
- so the outer electrons are less strongly attracted to the nucleus
- increasing covalent radius (this effect is also known as screening)
What are the two general trends of electronegativity?
- going down a group, electronegativity decreases
2. going across a period, electronegativity increases
Explain the trend of electronegativity going across a period
- going across a period the nuclear charge increases
- this causes the atom to attract bonded electrons more strongly
- resulting in an increase of electronegativity across a period
Explain the trend of electronegativity going down a group
- number of filled energy levels increases
- outer electrons are further from the nucleus and are less strongly attracted to the nucleus
- the inner electrons shield the outer electrons from the nuclear charge which means they are less strongly attracted to the nucleus
- resulting in a decrease in electronegativity as you go down the group
What are the two general trends of ionisation energy?
- going down a group, the ionisation energy decreases
2. going across a period, the ionisation energy increases
Explain the trend of ionisation energy going across a period
- going across a period, the nuclear charge is increasing
- the outermost electrons are therefore more strongly held and so the energy required to remove them (the ionisation energy) increases along the period
Explain the trend of ionisation energy going down a group
- energy levels increases
- the outermost layer is becoming increasingly further from the nuclear attraction
- the inner electrons reduce the attraction of the nucleus for the outermost electrons by creating a shielding effect
- hence, although the nuclear charge is also increasing, the energy required to remove an electron (the ionisation energy) decreases as you go down a group
