# Periodic table trends

• StephenDoty

#### StephenDoty

Hello everyone. I am currently studying the periodic trends in my chemistry I class. So I just want to make sure I understand the concepts.

Z effective= Atomic # - # of core electrons.
Z increases across a row and doesn't really change going down a group.

Size, radius, of atoms
the radius decrease from left to right and increase going down a group.

Ionization energies
Increases from left to right and from bottom to top of a group

electron affinity
becomes increasingly negative going from left to right and doesn't really change going down a group but can become increasingly negative going up a group

Reactivity
decreases going from left to right since ionization energies increase going left to right
and increases going down a group since ionization energies decrease going down a group.

## Answers and Replies

Z (atomic number) represents the number of protons (and + charges) in the nucleus of an atom, and in a neutral atom there is a equal number of electrons surrouding the nucleus. It is the electrons in the outermost 'shells' of the atom, i.e. those electrons that are most weakly bound, that determine the chemical properties of the atom (element).

Atomic mass is related to the total number of nucleons (protons and neutrons) in the nucleus of an atom. The atomic mass does not equal the mass of an equivalent number of nucleons because nucleons give up some energy (binding energy) when they combine to form more complex nuclei.

In the standard periodic table, Z increases from left to right, and from top to bottom.

This is a really good site for studying the periodicty of properties of the elements:
http://www.webelements.com/
http://www.webelements.com/periodicity/

e.g. http://www.webelements.com/periodicity/electron_affinity/

http://www.webelements.com/periodicity/atomic_radius/

do the chapter 23 Thermochemistry

Z (atomic number) represents the number of protons (and + charges) in the nucleus of an atom, and in a neutral atom there is a equal number of electrons surrouding the nucleus. It is the electrons in the outermost 'shells' of the atom, i.e. those electrons that are most weakly bound, that determine the chemical properties of the atom (element).

Atomic mass is related to the total number of nucleons (protons and neutrons) in the nucleus of an atom. The atomic mass does not equal the mass of an equivalent number of nucleons because nucleons give up some energy (binding energy) when they combine to form more complex nuclei.

In the standard periodic table, Z increases from left to right, and from top to bottom.

This is a really good site for studying the periodicty of properties of the elements:
http://www.webelements.com/
http://www.webelements.com/periodicity/

e.g. http://www.webelements.com/periodicity/electron_affinity/

http://www.webelements.com/periodicity/atomic_radius/

nuc

Why does A and Z diverge as the elements get bigger?