Chapter 7 Flashcards
How is the periodic table arranged?
The periodic table is arranged by:
• ascending atomic number
• periods- elements with the same number of electron shells are arranged in horizonal rows, periods, which means there are repeating trends in physical and chemical properties amoung these elements known as periodicity
• groups- elements with the same number of outer electrons are arranged in vertical columns giving them similar properties
How was the periodic table arranged historically?
Historically the periodic table was arranged in order of atomic mass by Mendeleev who also grouped the elements with similar properties leaving space for those undiscovered
How many blocks does the period table have?
Four the s, p, d and f blocks
S hold thier outer electrons in s orbitals
P hold thier outer electrons in p orbitals
D hold thier outer electrons in d orbitals
Definition of first ionisation energy
the energy required to remove one electron from each atom in one mole of gaseous atoms of an element form one mole of gaseous 1 + ions
Factors affecting ionisation energy
1) atomic radius- the greater the distance between the nucleus and outer electrons the less than nuclear attraction
2) nuclear charge- the more protons in the nucleus of an atom the greater the attraction to the outer electrons
3) electron shielding- electrons are negatively charged so in a shell electrons repel outer shell electrons. This shielding effect reduces attraction between the nucleus and outer electrons
Write the equation for first and second ionisation energy
First ionisation energy X(g) →X^+(g) + e^-
Second ionisation energy X^+ (g) → X^2+ (g) + e^-
What do second ionisation energies provide evidence for
second ionisation energies provide evidence for different electron energy levels and allows us to predict the number of electrons in each shell of an atom and its group because large jumps between ionisation energy suggest the electron is in a different shell
What are the trends in first ionisation energy down a group
first ionisation energy decreases down a group because as the group descends the number of field electron shells increase which has a result increases the shielding effect. Also so as electron shells increase so does atomic radius therefore the outer electrons have less attraction to the nucleus and this effect overweighs the increased nuclear charge
Explain the trends in first ionisation energy across a period
ionisation energy increases across a period because no new shells are added so shielding a similar but nuclear charge increases which increases the pull on outer electrons decreasing the radius therefore the increased nuclear charge and decrease the atomic radius make it harder to remove an electron so first ionisation energy increases
What is metallic bonding
Metallic bonding is a strong electrostatic attraction between cations and delocalized electrons the cations are fixed in a closely packed lattice surrounded by a sea of delocalised electrons
What are the properties of metals
1) good conductors when solid and when molten as the delocalized electrons are free to move and carry a charge
2) high melting points due to the strong metallic bonds which are affected by the number of delocalised electrons
3) insoluble due to the strength of the metallic bonds
What is a giant covalent structure
A giant covalent structure is a network of atoms bonded by strong covalent bonds
What is diamond and what are its properties
Diamond is a giant covalent structure with each carbon atom covalently bonded to four others giving a tetrahedral shape
Properties
1) very high melting point due to the large amount of energy needed to break the strong covalent bonds
2) it’s a non conductor as all electrons are covalently bonded and are not free to carry a charge
3) it’s in soluble as the covalent bonds are far too strong to be broken by interactions with solvents
What is graphite/ graphene and what are their properties
Graphite is a giant covalent structure where each carbon atom is covalently bonded to 3 others arranging it in flat hexagonal sheets with a weak dipole-dipole interactions between them graphene is one sheet of graphite.
Properties
1) very high melting point due to the strong covalent bonds within layers
2) conductor as each carbon atom has a delocalized electron which is free to move and carry a charge
3) insoluble due to the strong covalent bonds which are far too strong to be broken by interaction with solvents
What is the periodic trend in melting points over period 2 and 3
the melting point increases from group 1 to 3 as the metallic bonds get stronger as the number of delocalised electrons increase
There is a sharp increase between group 4 to 5 as they become giant covalent structures which have very high melting points
There is a sharp decrease from group 4 to 5 as they become simple molecular structures with low melting points
