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Trends in the Periodic Table
Transcript of Trends in the Periodic Table
A. Effective Nuclear Charge - corresponds to the number of protons in the nucleus
*as the atomic no. increases, ENC increases
B. Electron Shielding - when a shell is a full, those electrons shield the nucleus from the electrons which are further out.
C. Atomic Radius - 1/2 between the nucleus in two adjacent atoms
diameter of an atom ranges from about 1.4 x 10^-10
radius ranges from 7.0 x 10^-11 to 2.9 x 10^-10
Units used to express the measurement of an atom
angstrom (Å) - 1Å = 1.0 x 10^-10 m
picometer (pm) - 1 pm = 10^-12 m
L -> R in a row: radius decreases
*Why? As you go L -> R across a row, the atomic number increases, therefore the ENC increases. Since no new completed shells are added to provide electron shielding, the attractive force of the nucleus has a greater effect on the electrons, thus pulling the valence shell closer to the nucleus.
T -> B in a column: radius increases
*Why? As you go T-> B down a row, you add more complete shells to the atom, which provide more electron shielding. As a result, the attractive of the nucleus has less of an effect on the valence shell.
Ionization energy (IE) is the energy required to remove an electron from isolated, gaseous atom or ion in its ground state. The amount of energy required to remove the electron from the atom depends on how strongly the electron is attracted to the nucleus. Ionization energies measure how tightly electrons are bound in an atom.
Electron affinity (EA) - is the energy released when an incoming electron is finally added to an isolated atom or neutral atom in its ground state
Depends upon the electron configuration of the elements
The greater the tendency of an atom to accept electron, the more negative the electron affinity is
*L -> R electron affinity increases
*T -> B electron affinity decreases
*L-> R electron affinities become smaller (more negative)
*T -> B electron affinities become larger (less negative)
Why do columns IIA and VIII have positive values for their electron affinities (they don't want to gain electrons)?
*The elements in the column are diamagnetic, to all orbitals are filled with electron pairs (s orbitals in column IIA and p orbitals in column VIII). As a result. any added electrons would have to be unpaired which is a very unfavorable arrangement)
Why does column VA have such low electron affinity compared to its neighbors?
*The elements in this column have a half-filled p sublevel which is more favorable than a "lopsided" arrangement.
Electronegativity of an element is the attractive force of an atom for shared pair of electrons when chemically combined with another element.
In other words, how badly atom "wants" to gain electron
L -> R in a row: EN increases
T -> in a column: EN decreases
This electronegativity indicates that atoms of metals have a greater tendency to lose electrons than atoms of nonmetals and those of nonmetals have a great tendency to gain electrons.
Metallic property is the ability of atoms to lose electrons while the nonmetallic property is the ability of the atom to gain or accept electrons.
L -> R in a row: MP decreases
T -> B in a column: MP increases
Ions are electrically charged particles obtained from an atom or a chemically bonded group of atoms by adding or removing electrons
* higher IE - "harder" to remove the electrons
* lower IE - "easier" to remove electrons
First ionization energy - the amount of energy needed to remove the first electron from an atom.
Second ionization energy - the amount of energy needed to remove the second electron from an atom.
*L -> R in a row: 1st ionization energy increases
Why? As you go L->R across a row, the ENC increases with no additional shielding. As a result, the valence electrons are held more tightly by the nucleus
*T -> B in a column: 1st ionization decreases
Why? As you go T -> B down a column, the atoms have more shells. As a result, the effect of electron shielding is greater, and the valence electrons are held less tightly by the nucleus.
Anion - When an atom gains an electron, it becomes a negatively charged ion
- larger in size than their parent atoms because they have one or more additional electrons, but without an additional proton in the nucleus to help moderate the size.
Cation - When an atom loses an electron, it becomes a positively charged ion
- smaller than their parent atoms because they have lost electrons (sometimes the entire outermost energy level) and the electrons that remain behind simply don't take up as much room.