Chemical changes and Structure Flashcards
What is a metallic lattice sometimes called and what does a metallic lattice refer too?
Metallic lattice is sometimes just called metallic and refers to all the metals in the periodic table, including the transition metals.
What is the definition of monatomic?
Monatomic means a single atom.
What group is given the name monatomic and why?
Monatomic meaning “single atom” is the name given to the noble gases as they do not generally bond with other atoms as they have a full energy level of electrons.
Which elements can be described as having a covalent network bonding and structure?
The elements boron, carbon (graphite and diamond) and silicon which all sit close to each other in the periodic table, have the covalent network bonding and structure.
What are elements in the periodic table arranged in?
Elements are arranged in the periodic table in order of increasing atomic number.
What does the periodic table allow chemists to do?
The periodic table allows chemists to make accurate predictions of physical properties and chemical behaviour for any element, based on its position.
Describe the feature of the periodic table: groups.
Groups are vertical columns within the periodic table contain elements with similar chemical properties resulting from a common number of electrons in the outer shell.
Describe the feature of the periodic table: periods.
Periods are rows of elements arranged with increasing atomic number, demonstrating an increasing number of outer electrons and a move from metallic to non-metallic characteristics
What is the definition of atomic size (covalent radius)?
The covalent radius is a measure of the size of an atom.
The covalent radius is half the distance between the nuclei of two bonded atoms of the element and gives a measure of the size of an atom.
What is the definition of periodicity?
Periodicity is the occurrence of patterns in the periodic table.
What is the trend in covalent radius across a period (from left to right)?
Across a period left to right the covalent radius decreases.
Explain the trend in covalent radius across a period(from left to right).
Across a period left to right the covalent radius decreases. This is because atoms with the same period have the same number of occupied energy levels but there is an increase of one proton in the nucleus from one element to the next. This increased positive charge on the nucleus increases the attraction for the electrons in the outer energy level and they are pulled closer to the nucleus, making atoms get smaller across a period.
What are the compounds with a covalent network bonding and structure?
Silicon carbide and silicon dioxide are the only compounds with a covalent network structure.
What is the trend in covalent radius down a group?
Down a group the covalent radius increases.
Explain the trend in covalent radius down a group.
Down a group the covalent radius increases. Elements within the same group have one more occupied energy level with each succeeding element. Although the nuclear charge increases, its effect is outweighed by the increased number of energy levels.
What is ionisation energy?
Ionisation energy is a measure of the ease in which atoms of an element lose electrons and become positive ions.
What is the first ionisation energy?
The first ionisation energy is the energy required to remove one electron from each atom of one mole of gaseous atoms.
The first ionisation energy of any element can be represented in a chemical equation as:
M(g) → M+(g) + e-
Where M represents the symbol of any element and the electron on the right hand side of the arrow shows it has been lost from the atom.
What are ionisation energies measured in?
Ionisation energies are measured in kJ mol-1 (kilojoules per mole). They vary in size from 381 (which you would consider very low) up to 2370 (which is very high).
Why does helium not normally form a positive ion?
The reason that helium (1st I.E. = 2370 kJ mol-1) does not normally form a positive ion is because of the huge amount of energy that would be needed to remove one of its electrons.
What is the second ionisation energy?
The second ionisation energy is the energy required to remove one electron from each singly positive ion of one mole of gaseous ions.
What can the second ionisation be represented as?
The second ionisation of any element can be represented in a chemical equation as:
M+(g) → M2+(g) + e-
There are third and fourth ionisation energies etc if the atom has a sufficient amount of electrons.
Are ionisation energies endothermic or exothermic?
Ionisation energies are always endothermic.
What is meant by endothermic?
a reaction or process that takes in heat energy is described as endothermic.
What is meant by exothermic?
a reaction or process that releases heat energy is described as exothermic.
Why are ionisation energies always endothermic?
Energy is required to remove an electron from any atom because there is an attractive force between the nucleus and the electron being removed which has to be overcome.
What is the general trend in ionisation energy across a period (left to right)?
The general trend is that across a period (left to right) the ionisation energy increases.
What is the trend in ionisation energy down a group?
The general trend in ionisation energy down a group is that it decreases.
Explain the trend in ionisation energy across a period.
Across a period from left to right, the ionisation energy increases as with each successive element one proton is added so the nucleus is becoming more positive. This increase in nuclear charge exerts a greater electrostatic attraction (pull) on the electrons and therefore more energy is required to remove electrons.
Explain the trend in ionisation energies going down a group?
Going down a group, the ionisation energy decreases. This is because with each successive element there is an extra occupied energy level so the electron being removed is further away from the nucleus. Also, this electron is more shielded from the positive charge on the nucleus, by the inner occupied energy levels. This increased distance and shielding or screen affect of the outer electrons from the nucleus, make the electrostatic attraction weaker and the electrons are more easily removed.
What is electrostatic attraction?
Electrostatic attraction simply describes the attraction of oppositely charged particles.
What is the trend in subsequent ionisation energies?
Second and third ionisation energies are larger than the first because the extra positive nuclear charge(s) has greater electrostatic attraction for the outer electrons.
If an electron is being removed from a full outer energy level is the ionisation energy high or low?
If an electron is being removed from a full outer energy level, the ionisation energy is exceptionally high.
Why is the second ionisation energy much higher than would be expected?
The second ionisation energy is much higher than would be expected because this electron is being removed from a full outer energy level which is
- a very stable arrangement
- closer to the nucleus
- less screened from the nucleus as there are fewer inner electron energy levels.
What is electronegativity?
Electronegativity is a measure of the attraction an atom involved in a bond has for the electrons of the bond.
What is meant by high electronegativity?
The higher the electronegativity, the more strongly the atom/nucleus attracts electrons towards it.
Where can the electronegativity values be found?
Electronegativity values can be found in the data booklet as they show a similar trend to ionisation energy and the explanations are also similar.
What is the trend for electronegativity across a period?
Across a period left to right, electronegativity increases.
What is the trend for electronegativity down a group?
Down a group electronegativity decreases.
Explain the trend in electronegativity across a period (from left to right).
Across a period left to right, electronegativity increases since the nuclear charge increases, making the nucleus have a stronger electrostatic attraction for electrons.
Explain the trend in electronegativity down a group.
Down a group electronegativity decreases since atomic size increases due to the increase in the number of occupied energy levels and the electrons are further from the nucleus. The nucleus is also more screened by inner occupied energy levels. Both these factors reduce the electrostatic attraction between the nucleus and the electrons.
