C2 The Periodic Table Flashcards
How and why is the modern periodic table different from Mendeleev’s?
In the modern periodic table, elements are arranged in order of atomic (proton) number. Back then protons hadn’t been discovered yet so Mendeleev ordered the elements in his table in order of atomic mass. However this meant that elements could be in the wrong order due to the presence of isotopes.
Also the modern periodic table contains group 0 (noble gases), which hadn’t been discovered during Mendeleev’s time.
How did Mendeleev develop the first modern periodic table?
He arranged all the elements in increasing atomic weight, however he would switch the order of some elements so they fitted the same patterns of other elements in the same group. He also left gaps in his table for undiscovered elements. Several years later new elements were discovered and they matched the properties that Mendeleev predicted.
Which scientist developed the first modern periodic table?
Dimitri Mendeleev
Why was Newlands’ law of Octaves disregarded by other scientists?
By always sticking to atomic weight, some elements grouped together had totally different properties
What was Newlands’ law of Octaves?
He arranged elements in increasing atomic weights and saw that every 8th element reacted in a similar way.
What was Johann Döbereiner’s theory of “Triads”?
- He thought that elements with different properties occurred in threes.
e.g. Sodium Lithium and Potassium all react rapidly
with water.
Or Chlorine Bromine and Iodine were all reactive
non metals
Give 3 uses of transition metals
Iron - mixed with other elements to make steel
Copper - Electrical wires, water pipes
Gold - Malleable and shiny
What is the only transition metal that is a liquid at room temperature?
Mercury
Are transition metals more or less reactive than group 1 metals
Much less
Do transition metals have low or high densities?
High
Do transition metals have low or high melting and boiling points?
High
Are transition metals hard or soft?
Hard
Describe the properties of the transition elements
- Hard and strong (iron)
- High melting and boiling points
( except mercury which is a liquid at room temp) - High densities
- Not very reactive; much less than group 1
- Form ions with different charges
- Form coloured compounds
- Can be used as catalysts
- Malleable
Cl2 + 2KBr ——– 2KCl + Br2
[ What type of reaction is this? ]
A displacement reaction, a more reactive halogen is displacing a less reactive one from an aqueous solution
Explain why reactivity decreases down group 7
There’s a greater distance from the nucleus down the group, and the outer electrons are shielded by the internal shells. This means that there is less attraction to the positive nucleus, and the outer energy level is unlikely to receive an electron.
(Why Cl2 is more reactive than F2)
What is a displacement reaction?
A more reactive element displacing “pushing out” a less reactive element from a compound
“Reactivity _______ down group 7”
[Fill in the blank}
Decreases
Are group 7 metals toxic?
Yes
Do group 7 elements have high or low melting and boiling points?
Low
Are group 1 metals good or poor conductors of electricity?
Good
Describe the properties of the Halogens
- Toxic
- Non metal
- Poor conductors of heat and electricity
- Diatomic (bonded covalently)
- Very reactive
- Reactivity decreases down the group
- Low melting and boiling points
What is electron shielding?
An outer electron’s attraction to the nucleus being reduced due to a shielding effect from the inner shells
Explain why reactivity increases down group 1
As you go down the group, the atoms get larger, and the outermost electron experiences less electrostatic attraction towards the positive nucleus as the distance between the outer electron and nucleus increases.
The outer electron also experiences an electron shielding effect.
Do group 1 metals have high or low densities?
Low
Are group 1 metals soft or hard?
Soft
Do group 1 metals have high or low melting and boiling points?
Low
Why are the group 1 metals stored in oil?
It stops them from reacting with moisture in the air
Describe properties of the group 1 alkali metals
- Very reactive
- Low densities
- Soft
- Low melting and boiling points
- React vigorously with water and halogens
- Good conductors of electricity and heat
Name properties of the noble gases
- Highly unreactive
- Full outer shells
- Monatomic
Explain, in terms of electronic structure, why fluorine is the most reactive element in group 7 (3)
- Fluorine is the smallest atom
- And therefore experiences the smallest electron
shielding effect between the nucleus and outer shell - So it can gain an electron to its outer shell more
easily
What did Niels Bohr discover?
That electrons orbit the nucleus in energy levels (shells)
Explain how James Chadwick’s work on the atom led to a better understanding of isotopes (3)
- Chadwick proved the existence of neutrons
- Isotopes have the same proton number but a
different neutron number
(Improving understanding of atoms)
What happens to the melting point as you move down group 7?
It increases
What are the states of all the halogens at room temperature?
Fluorine - Gas Chlorine - Gas Bromine - Liquid Iodine - Solid Astatine - Solid
What does iodine form when heated?
A purple vapour
What happens to the boiling point of each noble gas as you go down the group?
It increases
What are the properties of non metals?
- Form negative ions
- Brittle
- Poor electrical and thermal conductors
- Low melting and boiling points
How did knowledge of protons and electrons allow chemists to place elements in the correct order? (3)
- Number of protons = number of electrons
- Number of shells gives the period
- Reactions/chemical properties depend on outer
electrons
Why did many chemists disagree with Mendeleev’s table in 1869?
- It had metals and non metals in the same group
- Group 1 contained copper and silver (were unreactive)
- Mendeleev left gaps (many chemists believed that there
were no more elements to discover) - Mendeleev reversed the order (for some elements)
How did Mendeleev know that some elements remained undiscovered?
When elements were arranged consecutively they would be in the wrong groups/ properties wouldn’t correspond
How did Mendeleev know that some elements remained undiscovered?
When elements were arranged consecutively they would be in the wrong groups/ properties wouldn’t correspond
Describe what would be seen in a reaction between sodium and chlorine
- Flame
- (white) solid forms
- colour of gas / chlorine
disappears / fades
