Topic 3 & 13 - Periodicity Flashcards
What are the rows in the periodic table called?
Periods
What are the columns in the periodic table called?
Groups
What do the period and group numbers give information about?
The period number gives the number of occupied electron shells
The group number gives the number of electrons in the outer shell
What happens to the nuclear charge experienced by an atom’s outer electrons in the periods and groups of the periodic table?
- Increases with the group number of the element
- Increases across a period
- Stays the same down a group
How is the atomic radius defined?
Measured as half the distance between neighbouring nuclei
Where are transition elements located in the periodic table?
Between groups 2 and 3
What is the trend in atomic radii?
- Increases down a group as the no. of occupied electron shells increases
- Decreases across a period because the attraction between the nucleus and other electrons increases as the nuclear charge increases
Where do we get the nuclear charge from?
The atomic number of each element
What are can be said about the sizes of ions?
- Positive ions are smaller than their parent atoms
- Negative ions are larger than their parent atoms
What are the trends ionic radii?
- Decrease from groups 1 to 4 for positive ions
- Decrease from groups 4 to 7 for negative ions
- Increase down a group as the no. of electron shells increases
What are the trends of ionisation energies?
- Increase across a period
- Decrease down a group
- Is the reverse of atomic radii
What is electronegativity?
The ability of an atom to attract electrons in a covalent bond
What are the trends in electronegativity?
- Increases from left to right across a period
- Decreases down a group
What are the trends in melting points?
- Decrease down group 1 (metallic structures, weaken with distance)
- Increase down group 7 (molecular structures, increase with no. of electrons)
- Generally rise across a period and reach a maximum at group 4 and fall to a minimum at group 0
Summarise the trends in the periodic table
Direction of the arrow indicates increase
cyan = atomic radius
pink = first ionisation energy
purple = electronegativity
grey = ionic radius
gold = melting point
What determines the chemical properties of an element?
Mostly the number of electrons in the outer shell
What are the chemical properties of group 0 elements? (noble gases)
- Colourless gases
- Monoatomic: exist as single atoms
- Very unreactive
- Have a stable octet
What are the chemical properties of group 1 elements? (alkali metals)
- Highly reactive (usually stored in oil to prevent reaction with ail)
- Form ionic compounds with non-metals
- Form single charged ions
- Reactivity increases down a group (lower ionisation energies
How do group 1 elements react with water?
- Produce hydrogen and a metal hydroxide
- Resulting solution is alkaline
- Reaction becomes more vigorous down a group
Lithium:
- floats and reacts slowly
- releases oxygen and keeps its shape
Sodium:
- reacts vigorously and the heat produced melts the metal into a bubble that moves around the surface of the water
Potassium:
- reacts more vigorously
- sets the hydrogen produced in fire
- produces a lilac flame and moves excitedly
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What are the physical properties of group 1 elements?
- Good conductors of electricity
- Have low densities
- Have grey shiny surfaces when freshly cut with a knife
What are the physical properties of group 7 elements?
- Coloured
- Show a gradual change from gases, to lidquid, to solids
What are the chemical properties of group 7 elements? (halogens)
- Very reactive non-metals
- Form ionic compounds with metals or covalent compounds with other non-metals
- Reactivity decreases down the group
- Exist as diatomic molecules
- Attraction for electrons is greatest in the smallest atom, F
Describe the reations between alkalis and halogens
- Form ionic halides
What happens in the displacement reaction of KBr with chlorine?
2 KBr(aq) + Cl2(aq) → 2 KCl(aq) + Br2(aq)
- the solution turns orange because Br is orange
What is the displacement reaction between iodine and bromine?
2 I–(aq) + Br2(aq) → 2 Br–(aq) + I2(aq)
- The solution darkens due to formation of iodine
What happens in a reaction between a more reactive and less reactive halogen?
The more reactive halogen displaces the ions of the less reactive halogen