Reactions and trends Flashcards
Use a Roman numeral to indicate the oxidation number of an element in a compound. For example
iron (III) Chloride
iron (II) Chloride
Redox reaction
A redox reaction involves something being oxidised and reducted
Oxidation - loss of electrons
increase in oxidation number
Reduction - gain of electrons
decrease in oxidation number
Remember OILRIG - Oxidation is loss Reduction is gain
Redox reactions always have something that gains electrons while the other losses electrons. If there are neither it’s not a redox reaction.
What is the oxidation numbers of elements
0
In a compound it’s also 0
Oxidation number of a monatomic ion
Is the same charge as the ion.
Redox reactions by colour changes
cl2 + 2NaI —> i2 + 2NaCl
Nai = colourless
i2 = red brown
2FeCl3 + 2Nai —> 2FeCl2 + 2NaCl + i2
FeCl3 = yellow
Nai = colourless
i2 = red brown
Mno^- 4 + 8H^+ 5fe^2+ —> mn^2+ + 4H2O + 5fe^2+
MnO^- 4 = purple
5fe^2+ = pale green (practically colourless)
Whole end products are colourless except mn^2 which is a pale pink.
oxidising agent
a substance that oxidises another substance and is itself reduced
Example
MnO^- 4 has an oxidation number of +7 and can gain 5e^- from another substance to form Mn^2+
reducing agent
a substance that reduces another substance and is itself oxidised
Periodic Table Arrangement
arrangement of elements in periods and groups and in order of
increasing proton number/ atomic number
Describe the change from metallic to non-metallic character across a period
The change from metallic to non-metallic character across a period is due to the tendency to gain or lose electrons in chemical reactions. Metals tend to lose electrons and non-metals tend to gain electrons. The tendency to gain electrons increases across a period due to an increase in the nuclear charge and decrease in the atomic size. Hence, the non-metallic character increases across a period
Describe the relationship between group number and the charge of the ions formed from elements in that group
The relationship between group number and charge on ion of an element is as follows
For elements in groups 1, 2 and 3, the number of electrons lost is the same as the group number.
For elements in groups 6 and 7, the charge on the ion is equal to (8 minus group number).
The number of charges on an ion formed by a metal is equal to the metal’s group number.
The number of charges on an ion formed by a nonmetal is equal to the group number minus eight.
Sodium is in group 1 of the periodic table. A sodium atom loses one electron to form a sodium ion with a charge of 1+.
Explain similarities in the chemical properties of elements in the same group of the Periodic Table in terms of their electronic configuration
The electronic configurations of atoms help explain the properties of elements and the structure of the periodic table. Elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell (valence electrons).
An example of this is all elements in group 1 have one valence electron and they are all very reactive metals while group 7 elements have 7 valence electrons but are very unreactive.
Explain how the position of an element in the Periodic Table can be used to predict its properties
Some of these trends include atomic size, ionization energy, electronegativity, electron affinity, reactivity of metals and nonmetals, and number of outer electrons. These trends can be explained and understood by analyzing the electron configurations of the elements.
Describe the Group I alkali metals, lithium, sodium and potassium, as relatively soft metals with general trends down the group, limited to:
(a) decreasing melting point
(b) increasing density
(c) increasing reactivity
Lithium - melting point = 180
0.535g/cm^3
Lithium reacts fairly slowly, fizzing.
Sodium - melting point = 98
0.968g/cm^3
Sodium reacts more quickly, generating enough heat to melt itself and to occasionally ignite the hydrogen gas, producing a yellow-orange flame characteristic of sodium.
potassium - melting point = 63
0.856g/cm^3
Potassium reacts violently, immediately bursting into a flame which has the characteristic violet color of potassium.
The order of reactivity of these elements is potassium > sodium > lithium.
Describe the Group VII halogens, chlorine, bromine and iodine, as diatomic nonmetals with general trends down the group, limited to:
(a) increasing density
(b) decreasing reactivity
Chlorine - density = 3.214g/cm^3
Chlorine is a highly reactive element that is a good oxidation agent.
Bromine - density = 3.12 g/cm^3
Very reactive element, it is between chlorine and iodine in the reactivity scale.
iodine - density = 4.94g/cm3
Least reactive of the halogens
State the appearance of chlorine, bromine and iodine
chlorine, a pale yellow-green gas
bromine, a red-brown liquid
iodine, a grey-black solid
Describe and explain the displacement reactions of halogens with other halide ions
Halogens react with metals to form halide salts through a process called displacement.
In a displacement of halogen, a more electronegative halogen displaces a less electronegative halogen from its halide solution.
The halide ions of the less electronegative halogen act as the reducing agent. They lose their electrons and are oxidised to form halogen molecules.
Halogens which are positioned further up in group 17 act as oxidation agents.
These halogens undergo reduction and are reduced to halide ions.
The halide ions which are positioned further down in group 17 act as reducing agents.
Describe the transition elements that have high densities
osmium, gold and mercury
Describe the transition metals that have the highest melting points
iron, chromium and copper
Describe the transition metals that form coloured compunds
Cobalt (II) - pink
Copper (II) - blue
Iron (III) - brown
Iron (II) - green
Permanganate - purple
Dichromate - orange
Chromate - yellow
Nickel (II) - green
Chromium (III) - green
Mangnanese ion (II) - pink
Describe the transition metals that often act as catalysts as elements and in compounds.
iron, copper and chromium
Iron will in some reactions
Describe transition elements as having ions with variable oxidation numbers, including iron(II) and iron(III)
Transition metals are known for having variable oxidation states because they have partly filled d orbitals in their outer electron shell, which allows them to form a range of ions with different charges. This property is unique to transition metals and sets them apart from other elements in the periodic table.
characteristics noble gases
Almost Non-reactive.
High ionization energies.
Very low electronegativities.
Low boiling points (all monatomic gases at room temperature)
No color, odor, or flavor under ordinary conditions.
Non-flammable.
At low pressure, they will conduct electricity.
They have no valence electrons which makes them not very reactive.
physical properties of metals
Shiny
High melting points
Good conductors of electricity
Good conductors of heat
High density
Malleable
High boiling point
physical properties of nonmetals
Low melting points
Poor conductors of electricity
Poor conductors of heat
Low density
Brittle
low boiling point
Describe the general chemical properties of metals, limited to their reactions with:
(a) dilute acids
(b) cold water and steam
(c) oxygen
Metal + dilute acid → Salt + Hydrogen gas
if a metal reacts with cold water, then metal hydroxide is produced.
metal + oxygen → metal oxide. Rust is a form of iron oxide and it forms slowly when iron is exposed to air.
Reactivity series
potassium
sodium
calcium
magnesium
aluminium
carbon
zinc
iron
hydrogen
copper
silver
gold
potassium, sodium and calcium with cold water reaction
Potassium (K) and Sodium (Na) react vigorously with cold water and hydrogen gas produced immediately catches fire while calcium (Ca) reacts with cold water but the reaction is not that vigorous.
magnesium with steam reaction
Magnesium burns in steam creating a white magnesium oxide and hydrogen gas
magnesium, zinc, iron, copper, silver and gold with dilute hydrochloric acid reactions
There is no reaction between copper, silver and gold with dilute hydrochloric acid.
When reacting with hydrochloric acid:
Magnesium creates magnesium chloride and hydrogen gas is released.
Zinc creates zinc chloride and releases hydrogen gas.
When hydrochloric acid reacts with iron filings iron chloride or ferrous(II) chloride is formed and hydrogen gas is released.
Displacement reactions
Displacement reactions occur when a more reactive element displaces, or pushes out, a less reactive element from a compound that contains the less reactive element.
Oxidation number rules
Oxidation number of elements in their uncombined state is 0.
Oxidation number of a monatomic ion is the same as the charge on the ion
Sum of oxidation numbers in a compound is 0.
The sum of the oxidation numbers in an ion is equal to the charge on the ion.
