Ch7: Trends In The Periodic Table Flashcards
What is Atomic radius (covalent radius)?
Half the distance between the nuclei of two atoms of the same element that are joined togetherby a single covalent bond
What is the distance of atomic radius nknown as and why do we use atomic radius?
Known as bond length
We use it because it is not possible to measure the distance between the nucleus and the outermost electrons of an atom due to Heisenberg’s Uncertainty Principle
What is bond length?
Measured by techniques such as x-ray diffraction and electron diffraction
What group in the periodic table have no atomic radii values?
Noble gases
Because they do not form covalent bonds with one another
Trends with atomic radius
Down: increase
Across: Decrease
Why does atomic radius increase down the groups?
-More energy levels are introduced down the group, therefore atomic radius increases because the outer electrons are becoming further away from the nucleus
-Screening effect (outer electrons are shielded from the positive charge of the nucleus by inner ones)
Why does atomic radius decrease across a period?
-Increase in effective nuclear charge (No. of protons increase, more attractive force on outer electrons)
-No increase in screening effect (no additional shells across a period)
What is first ionisation energy?
The minimum energy required to completely remove the most loosely bound electrons from a neutral gaseous atom in its ground state
X -> X+^ + e-^
Trends with ionisation energy
Down: decrease
Across: Increase
Why does ionisation energy decrease down the groups?
-Increasing atomic radius
-Screening effect of inner electrons
Why does ionisation energy increase across the periods?
-Increasing effective nuclear charge
-Decreasing atomic radius
What causes exceptions to a general trend across a period?
-Ionisation energies are higher than expected due to extra stability in filled or half-filled sublevels
-More stability makes it harder to remove the outermost electrons
What is s econd Ionisation energy?
The energy requires to remove an electron from an ion with one positive charge in the gaseous state
X+ -> X2+ + e-
What are general points on ionisatio energies?
-Steady increase as electrons are removed
-Removing electrons from a new energy level, a large increase is seen
-Removing electrons from a new sublevel, a substantial increase is seen
What is electronegativity?
The relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond
Trends with electronegativity?
Down: Decrease
Across: Increase
Why does electronegativity decrease down the groups?
-Increasing atomic radius (Atomic radii increases, outer electrons further away, less attraction between nucleus and shared pair of electrons)
-Screening effect (Increasing nuclear charge cancelled out by screening effect, outer electrons shielded from attractive forces of positive nucleus, attraction force decreases down groups)
Why does electronegativity increase across the periods?
-Increasing nuclear charge (No. of protons increase across periods, attraction between nucleus and outer electrons also increases)
-Decreasing atomic radius (Outer electrons beome closer to nucleus, therefore greater attraction)
Alkali Metals trends
1. Reactivity increases?
2. How reactive?
3. Melting points?
4. How is it stored?
- Reactivity increases down
- Very reactive
- Low melting points
- Stored under oil or in a glass with air removed
Chemical reactions with Alkali Metals:
1. With oxygen
2. With water
3. With acid
- Forms oxides
- Form the hydroxide of the metal and give off hydrogen gas
- Forms explosive substances
Trends in Halogens:
1. Reactivity increases?
2. How reactive
- Reactivity increases up
- Quite reactive
Chemical reactions with halogens
The more reactive halogen displaces the less reactive halogen from the solution of its ions
E.g. chlorine gas is bubbled through solution of bromide ions, chlorine takes an electron from bromide
Trends in alkaline earth metals
Each element, as you go down, reacts more and more with water
Reason= ionisation energies decrease down the group
Trends with noble gases
Unreactive
Boiling points steadily increase when going down the group due to increasing atomic radius and more van der waals
