Unit 1 Flashcards
What does the term periodic describe in chemistry?
Periodic describes a pattern that repeats itself at regular intervals
Explain what is meant by the term covalent radius?
Covalent radius is a term that is used to describe half of the distance between two nuclei of atoms joined by a covalent bond - covalent radius must be used as an estimate of atomic size as we cannot measure the distance between the nucleus of an atom and the outermost electrons as electrons are constantly moving
Explain why Covalent radius can be described as a periodic property?
As it is a pattern that repeats itself at regular intervals in the periodic table as you go down the groups in the periodic table the covalent radius will increase and as you go across the the periods of the periodic tables the covalent radius will decrease.
Explain why the covalent radius of an atom increases as you go down the groups in the periodic table?
As you go down the group in the periodic table this causes the number of electrons to increase. This increase in the number of electrons causes the shielding effect to take place whereby the increased number of electrons reduce the forces of attraction experienced by the outermost electrons to the nucleus this causes the outermost electron shell to be distanced further away from the nucleus causing the distance between two nuclei in a covalent bond to increase. The increased number of electron shells also means that there will be an increased number of outer shell electrons which increase covalent radius as more electron shells means a larger covalent radius.
Explain why the covalent radius of atoms decreases as we go across the periods in the periodic table?
As we go across the periods in the periodic table this means that the number of protons in the nucleus of the atom increases. This increased positive charge of the nucleus means that outer shell electrons experience a greater force of attraction towards the positive charge of the nucleus this causes the distance between the nuclei of atoms joined by a covalent bond to decrease as the electron shells move closer to the nucleus.
Define what is meant by the term electronegativity?
Electronegativity is defined as a measure of the ability of an atom involved in a chemical bond to attract the electrons in the bond.
Explain the properties of an element that is said to have a high value of electronegativity?
Elements with high electronegativity have a strong attraction for electrons in the bond (bonding electrons)
Explain the properties of an element that is said to have a low value of electronegativity?
Elements that have low values of electronegativity have a weak attraction for electrons in the bond
Explain why electronegativity can be described as a periodic property?
Electronegativity can be described as a periodic property as it repeats itself at regular intervals such as going across a period the electronegativity will increase and going down a group the electronegativity of the element will decrease.
Explain why electronegativity increases going across a period of the periodic table?
As you go across a period of the periodic table the values for electronegativity will increase as the number of protons in the nucleus of the atom will increase. The increased nuclear charge causes bonding electrons to be more strongly attracted by the increased positive charge meaning the value of electronegativity will be increased.
- Size of the atom will also decrease as the atom goes across a period this means that the bonding electrons will be more strongly attracted to the positive nucleus.
Explain why the values of electronegativity decrease as you go down the group of the periodic table?
As you go down a group the number of electrons and the number of electron shells increases this causes the screening effect to take place where inner electron shells reduce the forces acting on the bonding electrons meaning the attraction of the nucleus for bonding electrons is decreased as the atom has more electron shells as the shielding effect increases
- another factor is that as you go down a group in the periodic table the size of the atoms increases which causes bonding electrons to experience a decreased force of attraction. Both of these factors outweigh the increases in nuclear charge going down the group.
How are the electrons in the nucleus held in place around the atom?
The electrons orbiting the nucleus are held in place by the electrostatic attractions between the negatively charged electrons and the positively charged nucleus
Explain why an atom will never simply give away an electron?
Atoms do not give away electrons and to remove an electron from an atom energy will always be required to break down the existing electrostatic forces of attraction between the outer shell electron and the positive nucleus. For this reason it will always be an outer shell electron that is removed.
Define the term ionisation energy?
Ionisation energy is defined as the energy required to remove one mole of outer shell electrons from one mole of gaseous atoms or Ions.
What must you always remember to do when writing ion electron equations for Ionisation energies of elements?
You must always include the gaseous state symbol (g) as ionisation only works on gaseous atoms or Ions. Also remember that when doing a second or third ionisation energy equation both sides of the equation will involve ions.
Explain why the second ionisation energy of an element will always be higher than the first ionisation energy of the element?
This is due to the fact that the number of protons that are present in the nucleus remains unchanged after ionisation - removing electrons has no effect on the positive charge of the nucleus hence the remaining electrons will experience an increased force of attraction when the number of electrons decreases meaning that the next ionisation energy will require more energy as more energy will be required to break down the stronger electrostatic attractions between the nucleus and outer shell electrons
Explain why the second ionisation energies of group one elements are so much higher than second ionisation energies of other groups of the periodic table?
As since lithium is a group 1 element removing two outer shell electrons requires removing an electron from a complete stable electron shell, and when a very stable full outer electron shell is broken it requires a great deal of additional energy to remove the electron.
Explain how we can calculate the energy required to remove multiple outer electron shells from an atom?
We can calculate the energy required to remove multiple electrons by adding together the values for each ionisation of the element.
IE the energy required to remove 2 moles of electrons from one mole of gaseous atoms would be equal to the product of the first ionisation energy and the second ionisation energy.
Explain why first ionisation energy can be referred to as a periodic property?
As First ionisation energy has a pattern that repeats itself at regular intervals in the periodic table: as you go across a period of the periodic table the first ionisation energy of a gaseous atom increases, and as you go down a group in the periodic table the first ionisation energy of the gaseous atoms will decrease.
Explain why the first ionisation energy will increase going across a group in the periodic table?
As when we go across a group in the periodic table the number of protons in the nucleus increases hence the nucleus has an increased positive charge. As well as the decreased atomic size going across a period causes the outer electrons to be more strongly held to the nucleus meaning that more energy will be required to remove them
Explain why the first ionisation energy will decrease when going down a group in the periodic table?
Going down a group in the periodic table means that the atomic size increases and the number of electron shells increases. This causes the screening effect and the outermost electrons of the atom/ion experience a reduced force of attraction from the nucleus meaning that less energy will be required to remove them from the atom.
List the different types of bonding that can be found in chemical elements?
- Covalent discrete molecular
- Covalent network
- Monatomic gasses
- Metallic bonding
Describe the chemical properties of a metallic element?
Atoms are held together by strong metallic bonds in a lattice structure meaning that metallic elements have high melting and boiling points and are solids at room temperature. Metallic lattices conduct electricity because of the delocalised electrons that can be found in their structure.
Describe the chemical properties of a discrete covalent molecular element?
Discrete covalent molecular compounds are low melting point solids, they have strong covalent bonds between atoms however are held together by weak london dispersion forces between molecules meaning that they have low melting point and boiling points. They do not conduct electricity.
Describe the chemical properties of a covalent network element?
Covalent network elements are held together by vast networks of strong covalent bonds meaning that covalent network elements have high melting and boiling points and are solids at room temperature. They also do not conduct electricity.
Describe the chemical properties of monatomic gasses?
Monatomic gasses are held together by weak london dispersion forces between atoms meaning that they all have very low melting and boiling points which cause them to all exist as gaseous at room temperature. They too do not conduct electricity.
