Trends in the Periodic table Flashcards
What are groups
Groups are vertical column. Elements in the same group have the same number of electrons in their outer shell
what is a period
A period is a horizontal row. Elements in the have same number of shells
What is the atomic radius
Half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond
What is nuclear charge
The force of attraction between the positive protons in the nucleus and the negative electrons in the outer shell.
Why does atomic radius… down the groups of the periodic table
Increases
As you do down a group, each elements has one more shell of electrons than the previous. The negative outer electrons get further away from the positive nucleus. Screening effect increases
What is the screening effect
Down a group
The increase in nuclear charge as you go down a group is lessened by a screening effect. The electrons in the inner shells screen the outer electrons from the positive charge in the nucleus
The atomic radius … across a period because
Decreases
There a increase in effective nuclear charge
No increase in screening effect
What results in increasing nuclear charge
Number of protons increase, number of shells stay the same so the increase in effective nuclear charge,so there is a greater attractive force on the outer electrons
What is First ionisation energy
The minimum energy required to completely remove the most loosely bound electron from a neutral gaseous atom in its ground state
Ionisation energy … down a group because of
Decreases
Increasing screening effect.
Increasing atomic radius
Ionisation energy … across a period because of
Increases
Increasing nuclear charge
Decreasing atomic radius
Why do some elements have higher first ionisation energy?
These elements would have full/ half full sublevels. Full or half filled sublevels give an atom extra stability so more energy is required to remove an electron
What is second Ionisation energy of a atom
The energy required to remove an electron from an ion with one positive charge in the gaseous state.
What is the formula for second ionisation energy
X+(g) —-> X2+(g) + e-
( small 2+)
X= element
g= state of matter
What is the first, second and third ionisation energy of potassium
K(g) —-> K+(g) + e-
K+(g) —> K2+ (g) + e-
K2+(g) —> K3+ (g) + e-
Why is there a large increase in ionisation energy whenever electrons are removed from a new sublevel or every level?
Decreased shielding effect
What is electronegativity
The relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond
What happens to electronegativity when going down group and why
Electronegativity decreases going down a group.
1.increasing atomic radius
2. Increasing screening effect.
What happens to electronegativity values across a period
Electronegativity increases going across a period.
1 Increasing effective nuclear charge
2 Decreasing atomic radius
What do the chemical properties of an element depend on?
depends on their type of chemical bonding. How an element forms a bond is due to the number of electrons in the outer shell
Why are Alkali Metals reactive
They have a low ionization energy, the readily lose the single electron in their outer shell
Where are Alkali metals found
They are found in compounds, not free in nature itself
Do the elements of group on lose their outer electrons easier or harder as you go down a group
Easier, because:
The atomic radius increases
Screening effect increases
Reactions of Alkali metals with water
They all react vigorously with cold water.
Hydrogen gas is given off, metal hydroxide is produced
Speed and violence of the reaction increases as you go down a group- increased reactivity
Describe the reaction of Lithium with water
Lithium floats, fizzes steadily and become smaller until it eventually disappears
Describe the reaction of Sodium with water
The sodium melts to form a ball that moves around on the surface of the water. It fizzes rapidly, the hydrogen produced may produce a orange flame before the sodium disappears
Word equation for reaction of Alkali metals with water
(element) + water —> (element) hydroxide + hydrogen
Equation for reaction of Alkali metals with water
(element) + H2O —> (element)OH + 1/2 H2
Reaction of alkali metals with Oxygen
When Alkali metals are cut they initially appear shiny grey but quickly become dull and white as they react with oxygen in the air- this is known as tarnishing
How Lithium reacts with oxygen
Lithium tarnishes slowly due to its relatively slow reaction with oxygen
How Sodium reacts with oxygen
Tarnishes quicker than lithium, its more reactive then Lithium
How Potassium reacts with oxygen
Potassium tarnishes so quickly its difficult to see potassium is actually a shiny metal.
Word equation for reaction of Alkali metals with oxygen
( element) + Oxygen –> (element) oxide
Equation for reaction of Alkali metals with oxygen
2(element) + 1/2 O2 —> (element)2O
In order for an atom to be stable what rule must it obey?
The octet rule, 8 electrons in the outer shell
When a Halogen element reacts what does it do
It gains one electron
Does the reactivity of halogens increase or decrease as you do down a group, and why?
Decreases,
The atomic radius increases
The effective nuclear charge decreases
What can the reactivity of the halogens be shown by?
Displacement reactions
Name and example of displacement reaction for the Halogens
When chlorine( as a gas or dissolved in water), is added to sodium bromide, the chlorine takes the place of the bromine. The chlorine is more reactive than bromine
What’s the word formula for a displacement reaction of chlorine and bromine
Chlorine+ sodium bromide-> sodium chloride +bromide
What do displacement reactions show.
A more reactive halogen displaced a less reactive halogen from a solution of one of its salts.the electronegativity decreases
What is an Oxidising agent
A chemical which causes another chemical to lose an electron and become positivity charged
what is a Redox reaction
One reactant has lost an electron and the other has gained an electron
Redox reactions of the halogens
The halogens are very reactive elements, they are too unstable to exists in a nature in a uncombined form.They often react by taking an electron from another element, they act as oxidising agents. The smaller a halogen atom, the stronger oxidising agent it is.
List the halogens in order of oxidising power
F >Cl >Br >I >At
What is the colour of Chlorine in water
Pale green
What is the colour of Bromine in water
Yellow/ orange
What is the colour of Iodine in water
Brown/red
What is the colour of Chloride ions in water
Colourless
What is the colour of Bromide ions in water
Colourless
What is the colour of Iodide ions in water
Colourless
What is a diatomic molecule
A molecule that is made up of two atoms of the same or different elements
What does AQ stand for in refrence to the state?
aqueous solution
What does the acronym OIL RIG stand for
Oxidation Is Loss, Reduction Is Gain
