C7 - Periodic table and energy Flashcards
Who was responsible for the periodic table
Dmitri Mendeleev
How did Mendeleev organise the periodic table?
-In order of increasing atomic mass
-Grouped according to similar physical and chemical properties
-Left gaps for undiscovered elements
-Switched tellurium and iodine
Why didn’t Mendeleev accept noble gasses were elements?
They did not react
How is the periodic table arranged now
-Increasing atomic number
-7 horizontal periods
-18 vertical groups
What are groups?
Vertical column on periodic table
Elements with similar chemical properties and same number of outer-shell electrons
What are periods?
Horizontal rows in periodic table
Show trend in (physical) properties across a period
What’s periodicity?
Repeating trend in properties of element across each period of the periodic table
Periodic trend in electron configuration in period 2 and 3
-Period 2: 2s sub-shell fills with 2e-, 2p sub-shell fills with 6e-
-Period 3: 3s sub-shell fills with 2e-, 3p sub-shell fills with 6e-
What are blocks
Correspond to highest energy subshell
S block
P block
D block
F block
How are blocks arranged
What does ionisation energy measure?
How easily an atom loses electrons to form positive ions
What’s first ionisation energy?
Energy required to remove one electron from each atom in one mole of gaseous atoms of an element of form one mole of gaseous 1+ ions
First ionisation formula of Na
Na (g) —> Na+ (g) + e-
What factors affect ionisation energy?
Atomic radius
Nuclear charge
Electron shielding
How does atomic radius affect ionisation energy?
Greater distance between nucleus and out electrons
Less nuclear attraction
How does nuclear charge affect ionisation energy?
More protons
Greater attraction between nucleus and outer electrons
How does electron shielding affect ionisation energy?
Electrons are negatively charged
Inner shell electrons repel outer shell electrons
Reduce attraction between nucleus and outer electrons
What is shielding?
Repulsion between electrons in different inner shells
Reduces net attractive forces between nucleus and outer shell electrons
What is second ionisation energy?
Energy required to remove one electron form each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions
Second ionisation energy formula of He
He+ (g) –> He2+ (g) + e-
What can successive ionisation energies tell you?
-Large difference in ionisation energy suggests e- is in a different shell
-number of e- in outer shell
What happens to first ionisation energy down a group?
Decreases
Why does first ionisation energy decrease down a group?
-Atomic radius decreases
-More shells so shielding increases
-Nuclear attraction decreases
-First ionisation energy decreases
What happens to first ionisation energy across a period?
Increases
Why does first ionisation energy increase across a period?
-Nuclear charge increases
-Atomic radius decreases
-Nuclear attraction increases
-First ionisation energy increases
Where does first ionisation energy fall in period 2?
-Beryllium to boron
-Nitrogen to oxygen
Compare Be and B
-2p sub shell in in B has higher energy that 2s sub shell in Be
-Therefore, e- in B is easier to remove
-First ionisation of B is less
Compare N and O
-Highest energy e- are in 2p sub shell in N and O
-Paired e- in 2p orbitals repel, making it easier to remove, in O
-Therefore, first ionisation of O is less than N
At room temperature what state are most metals?
Solid
What metal is not solid at room temperature?
Mercury - liquid
What’s a metallic bond?
Electrostatic attraction between positive metal ions and delocalised electrons
What is the structure and bonding of metals?
Giant metallic structure consisting of cations and delocalised electrons held together by metalling bonds
Properties of metals
-Strong metallic bonds
-High electrical conductivity
-High melting and boiling points
Explain the conductivity of metals
When voltage applied, delocalised electrons can move and carry charge
Explain the high melting and boiling points of metals
To overcome strong electrostatic force of attraction between cations and delocalised electrons
Are metals soluble
Insoluble
What is a giant metallic lattice?
3D structure of positive ions and delocalised electrons, bonded together by metallic bonds
What is a covalent bond?
Strong electrostatic attraction between a shared pair of electrons and nuclei of bonded atoms
What is a giant covalent lattice?
3D structure of atoms bonded together by strong covalent bonds
Properties of giant covalent structures
-High melting and boiling points
-Insoluble
Explain the solubility of giant covalent structures
Covalent bonds are too strong to be broken by interactions with solvents
Explain the melting and boiling point of giant covalent structures
Strong covalent bonds require high energy to overcome
Explain the electrical conductivity of giant covalent structures
Don’t conduct electricity - all 4 outer shell electrons used in covalent bonding
Which giant covalent structure do conduct electricity
Graphene
Graphite
Periodic trend in melting point across period 2 and 3
Increases across groups 1-14
Sharp decrease from 14-15
Comparatively low from groups 15-18
What does the sharp decrease in boiling points between group 14 and 15 indicate?
Change from giant structures to simple molecular structure
