- Atomic radius decreases
- electronegativity increases
- electron affinity increases
- ionization energy increases
Atomic radius is the size an atom of a given element. As you go left to right across the periodic table, protons are being added to the nucleus, meaning there is a higher positive charge to pull the electrons in, so the atoms get smaller.
Electronegativity is the ability of an atom to pull a bonding pair of electrons towards it when it's in a covalent bond. Atoms with a larger positive charge in the nucleus can more easily attract a bonding pair of electrons.
Electron affinity is the likelihood of a neutral atom of an element gaining an electron. All atoms want an octet of electrons, so as you move left to right across a period, electron affinity increases with number of valence electrons (until you get to the noble gases when the electron affinity drops because they already have a full octet). Metals on the lefthand side of the table have a low electron affinity because it is easier for them to get to an octet if they lose electrons. Halogens (group 7A) have a high electron affinity because if they gain an electron, they have a full octet.
Ionization energy is the energy it takes to remove an electron. Metals (lefthand side) have a low ionization energy because they want to lose an electron to get to a noble gas configuration. Halogens (and non-metals more generally) have a higher ionization energy because they're already close to having an octet and it's easier for them to gain an electron than it is to lose 7 electrons.
Note: The general trends for ionization energy and electron affinity have exceptions between groups 2A and 3A and groups 5A and 6A due to the filled and half-filled subshell effects