Chemistry - Trends, Isotopes, and Radioisotopes

Group

A column on the periodic table

Period

A horizontal row of elements in the periodic table

attraction and repulsion

Like poles repel and unlike poles attract

Protons

Positively charged particles

Electrons

Negatively charged particles

valence electrons

Electrons on the outermost energy level of an atom

inner electrons

electrons that fill all the energy levels of an atom except the valence level

Shielding effect

the reduction of the attractive force between a nucleus and its outer electrons due to the blocking effect of inner electrons

Atomic Radius

Size of an atom. The further that the valence electrons are from the nucleus, the larger the atom

atomic radius trend

Increases down a group decreases across a period. Increases down because you are adding another "ring". Moving left to the right across decreases because the increases the effective nuclear charge so electrons are pulled closer to the nucleus

ionization energy

The amount of energy required to remove an electron from an atom. Moving down a group decreases, and adds more energy levels, and the valence electrons are further from the nucleus and therefore less attracted to it, making it easier.

Moving left to right increases the number of protons; the clarence is more attracted to them, so it requires more energy to remove them.

first ionization energy

the energy required to remove the first electron from an atom

ex. Na (g)→Na+(g)+e−

second ionization energy

energy required to remove the second electron

ex. Na+(g)→Na2+(g)+e−

Electronegativity

The ability of an atom to attract electrons when the atom is in a compound.

Increases left to right the effective nuclear charge increases and the atomic size decreases, the positive protons in the nucleus are able to pull on the negative electrons more effectively.

Decreases as you move down the atomic size increases and the effective nuclear charge decreases, the positive protons in the nucleus are able to pull on the negative electrons less effectively.

electron affinity

Measures the energy released when an atom gains an electrons.

As you go down a group, the atomic size increases, meaning the outermost electrons are farther from the nucleus. The force of attraction between the nucleus and the outermost electrons becomes weaker because there are more electron shells between them, which makes it harder for the atom to pull in an extra electron.

Moving from left to right, the number of protons in the nucleus increases, which means a stronger positive charge. This stronger nuclear charge creates a greater pull on the electrons, making it easier for the atom to attract and gain an extra electron.

Exceptions:

Group 2 (e.g., Be, Mg) and Group 15 (e.g., N, P) elements have less negative or positive electron affinities because of their stable electron configurations.

Noble gases (Group 18) generally have no electron affinity because they are already stable and don't readily accept extra electrons.

Isotopes

Atoms with the same number of protons but different numbers of neutrons

Radioisotopes

Isotopes that have unstable nuclei and undergo radioactive decay.

Ionic

metal and nonmetal

covalent bond

A chemical bond that involves sharing a pair of electrons between atoms in a molecule. Non-metal + non metal