Chapter 7-Periodicity Flashcards
What did Lavoisier contribute to the modern periodic table?
He compiled the first list of elements (but included light and heat)
What did Doberine contribute to the modern periodic table?
He proposed the law of triads where the atomic mass of the middle element was the average of the two neighbouring.
What did Newlands contribute to the modern periodic table?
He partially organised it by atomic mass but created the law of octaves-an element will behave similarly to the eighth element following it leaving no gaps for undiscovered elements.
What did Mendeleev contribute to the modern periodic table?
He ordered elements periodically acccording to their properties and almost always by atomic weight.
What is periodicity?
The periodic trend in properties, repeating each period
What are metalloids?
Elements with properties of both metals and non-metals.
How does atomic radius differ down a group and along a period and why?
- Down a group atomic radius increases as more shells of electrons-greater distance to outermost shell
- Along a period atomic radius decreases as there is an increased nuclear charge, hence a stronger pull on electrons
What is the First ionisation energy?
The energy required to remove one mole of electrons from one mole of gaseous atoms to produce 1 mole of gaseous H+ ions.
What is the general formula for the first ionisation energy?
X(g) –>X⁺ + e⁻
What are the factors affecting first ionisation energy?
- Atomic radius
- Electron shielding
- Nuclear charge
What are the 6 trends for first ionisation energies across periods 2 and 3?
- Noble gases have the highest first ionisation energy
- Along a period the first ionisation energy increases
- Dip between atomic numbers 4 and 5 and 11 and 13
- Second dip between groups 7 and 8 and 15 and 16
- Huge drop between noble gas and start of next period
- First ionisation energy decreases down a group
Explain why noble gases have the highest first ionisation energy?
Noble gases have a full outer shell so a stable nucleus
Why do first ionisation energies generally increase along a period?
Increased nuclear charge as nucleus gets larger so increased attraction to electrons with the same shielding as same no. of shells
Why is there a dip in first ionisation energies between atomic numbers 4 and 5 and 12 and 13?
Elements in group 3 have electrons in the P orbital that are a greater distance from the nucleus so are easier to remove
Why is there a second dip in first ionisation energy between atomic numbers 7 and 8 and 15 and 16?
The orbitals in group 16 are double filled with electrons so there is electrostatic repulsion between the electrons, making it easier to lose an electon.
Why is there a huge drop in first ionisation energy between the noble gas and start of the next period?
The first electron to be ionised is in the next shell so there is much less attraction to the electron due to increased shielding and it being further away from the nucleus.
Why does the first ionisation energies decrease down a group?
Size of atom increases, there are more shells, greater shielding so lower attraction and ionisation energy
How do melting points change across a period from groups 1-3?
Melting point increases due to increased strength of metallic bonding caused by larger number of electrons contributing to the electron cloud on the metal ion and larger charge on the metal ion
Explain the high melting point of group 4 elements
Group 4 elements form giant covalent structures-lots of energy needed to break the covalent bonds.
How do melting points change across a period from groups 5-8?
Melting points generally decrease as structures are simple molecular however phosporus exists as P₄ and Sulfur as S₈ so sulfur (group 6) has a higher boiling point than phosphorus (group 5)
