Respuesta :
Answer:
- See below this long answer.
Explanation:
These are the main features of the periodic table that you will be able to relate with some property trends of the atoms like size, energy levels, valence electrons, electronegativity, and ionization energy.
A) Features:
1. Elements are arranged in increasing order of atomic number, i.e. number or protons.
2. Since atoms are neutrals, the number of electrons equals the number of protons, and, as result, the elements are arranged in increasing order of number of electrons.
3. The elements are arranged in 18 columns and 7 rows.
4. The rows are named period and correspond to the principal energy level (n): first row corresponds to n = 1, second row corresponds to n = 2, third to n = 3, and so on up to n = 7. The number of elements in each period are:
Period 1, n = 1, 2 elements
Period 2, n = 2, 8 elements
Period 3, n = 3, 8 elements
Period 4, n = 4, 18 elements
Period 5, n = 5, 18 elements
Period 6, n = 6, 32 elements (this includes the 14 lanthanides)
Period 6, n = 7, 32 elements (this includes the 14 lanthanides)
That makes a total of 118 elements.
5. The columns are named groups and they indicate the number of valence electrons
Group 1: 1 valence electron
Group 2: 2 valence electrons
Group 13: 3 valence electrons
Group 14: 4 valence electrons
Group 15: 5 valence electrons
Group 16: 6 valence electrons
Group 17: 7 valence electrons
Group 18: 8 valence electrons
Groups 3 through 12 includ the transition metals and due they have subshells that are not completely filled, their valence electrons vary.
More like a reference than as a rule these are the number of valence electrons for these groups.
Group 3: 3 valence electrons
Group 4: 2-4 valence electrons
Group 5: 2-5 valence electrons
Group 6: 2-6 valence electrons
Group 7: 2-7 valence electrons
Group 8: 2-3 valence electrons
Group 9: 2-3 valence electrons
Group 10: 2-3 valence electrons
Group 11: 1-2 valence electrons
Group 12: 2 valence electrons
B) Property trends
1. Atomic radius (size)
- Down a period (from left to right): due to the increase of the positive charge (number of protons) while the main energy level (n) does not change, the electrons in the valence shell feel a stronger atraction to the nucleus causing that the atomic radius decrease from left to right.
- Down a group (top to bottom): due to the increase of the main energy level, the outermost orbital is bigger and the atoms become bigger. Thus the trend is that the atomic radius increase when you go down a group.
2. First ionization energy
- Down a period (from left to right): due to the increase of the nuclear charge (such as explained above) the greater attractive force makes that, in general, the first ionization energy increase from left to right.
- Down a group (top to bottom): due to the increase in the size of the atom, , generally, the energy to remove an electron from the outermost shell, decrease.
3. Electronegativity
This is the relative ability to atract electrons in a covalent bond. It increases from left to right and from bottom to top: the most electronegative atoms is fluor.
