3.2.1 Define the terms first ionization energy and electronegativity
- first ionization energy is the minimum energy required to remove a mole of electrons from a mole of gaseous atoms to form a mole of gaseous ions
- electronegativity is the ability of an atom to attract a shared pair of electrons in a chemical bonds
- the higher the electronegativity, the more strongly an element will hold on to electrons in a chemical bond (elements are assigned values from 0 to 4 on the Pauling scale, with 4 being the highest)
3.2.2 Describe and explain the trends in atomic radii, ionic radii, first ionization energies, electronegativities, and melting points for the alkali metals (Li --> Cs) and the halogens (F --> I)
Atomic Radius:
Ionic Radius:
First Ionization Energy
Electronegativity
Melting Point
Atomic Radius:
- this radius is the distance from the center of nucleus of atom to the approx. outer boundary of valence shell
- atomic radius increases going down a group in the periodic table
- electrons fill more energy levels (shells) as you go down a group. Since there are more occupied, radius will increase
- shielding: The temporary decrease in attraction between electrons in outer shells and the nucleus due to interference from electrons in inner shells passing between outer electrons and the nucleus. Average radius slightly increases
Ionic Radius:
- cations are smaller than their neutral atom
- the atoms lose valence electrons, so there's one less shell than a neutral atom
- also, since there are fewer electrons than proton, each electron experiences greater attraction to the nucleus (radius decreases)
- anions are larger than their neutral atom
- more electrons are added to the same energy level
- electron to electron repulsion increases and ionic radius increases
- the # of protons is unchanged, so attraction per electron decreases, therefore radius greater than neutral atom
First Ionization Energy
- as you go down each group, the ionization energy required decreases for the same reasons as for the atomic radius trend
Electronegativity
- as you go down a group, electronegativity decreases for the same reasons as for the atomic radius trend
Melting Point
- melting point is the temperature at which a solid begins to turn into a liquid
- it depends on the type of element since they show different types of bonding (need to know the type of aggregate)
- across a period, elements can show behaviour changing from metallic to non-metallic
- in group 1, melting point decreases down the group as the atoms become larger and the strength of the metallic bond decreases
- in group 7, the Van der Waal's attractive forces between the diatomic molecules increase down the group so the melting points increase
3.2.3 Describe and explain the trends in atomic radii, ionic radii, first ionization energies, and electronegativities for elements across period 3
Atomic Radius:
Ionic Radius:
First Ionization Energy:
Electronegativity:
Atomic Radius:
- atomic radius decreases going across a period in the periodic table
- as you proceed from left to right, there are more protons in the nucleus
- electrons occupy the same number of shells in a certain period
- therefore, there's a stronger attraction between electrons and protons in nucleus so radius slightly decreases
- "effective nuclear charge" - not the # of protons but rather how well protons can pull
Ionic Radius:
- for group 1, 2, and 3 cations in the same period:
- from 1-3, the radii becomes smaller because there is an increasing # of protons to the same # of electrons
- for group 15, 16, and 17 anions in the same period:
- the radii decreases from 15-17 since there are the same number of electrons but increasing # of protons
- however, within a period, all ANIONS have a larger radius than all cations due to anions having less protons than electrons
First Ionization Energy:
- as you go across each period, ionization energy required increases overall for the same reason as atomic radius increasing
- this is a trend not a rule because although the energy overall increases, sometimes there's a drop from one element to another
Electronegativity:
- as you go across a period, electronegativity increases for the same reasons as atomic radius increasing
3.2.4 Compare the relative electronegativity values of two or more elements based on their positions in the periodic table
- comparing sodium (Na) and fluorine (F)
- fluorine is higher in the periodic table than sodium, so it has less energy shells
- thus, the electrons are closer to the nucleus and there's less shielding, increasing fluorine's electronegativity/ability to pull on a pair of shared electrons
- fluorine is also further down its period than sodium is within its respective period
- thus, fluorine has a greater effective nuclear charge and increased electronegativity
- thus, fluorine is more electronegative