lecture 6.3- periodic trends (honors)

Bellwork- Excited?

1s22s22p63s23p54s23d104p4

What element is this?

Does this electron configuration represent an atom in an excited state or in its ground state? Explain.

Bellwork- Excited?

1s22s22p63s23p54s23d104p4

What element is this? As

Does this electron configuration represent an atom in an excited state or in its ground state? Explain.

Bellwork- Excited?

1s22s22p63s23p54s23d104p4

What element is this? As

Does this electron configuration represent an atom in an excited state or in its ground state? Explain. This As atom is in an excited state; One of the four electrons in the 4p sublevel could relax because a lower energy 3p orbital is unfilled.

Lecture 6.3-

Periodic Trends

The atomic radius measures an atom’s size.

It is one half of the distance between the nuclei of two atoms of the same element when the atoms are joined.

Group and Periodic Trends in Atomic Size

In general, atomic size increases from top to bottom within a group and decreases from left to right across a period.

Across a period left to right

Atoms get smaller because there are more protons in the nucleus pulling the electrons in closer.

Down a group

Atoms get bigger because they have 1 more energy level (layer)

A neutral atom contains an equal number of protons and electrons.

When an atom gains or loses electrons it is no longer neutral.

It becomes a charged ion.

An ion has a charge.

If an atom or a compound becomes

charged it is called an ion

A positive ion is called a cation

A negative ion is called an anion

Positive+

Positive+

Positive+

Anakin

NEGATIVE

When an atom gains an electron it gains an additional negative charge.

A Chlorine atom will gain one electron to become a Chlorine anion.

Cle-_

An Oxygen atom will gain two electrons making an Oxygen ion with a charge of negative two.

Oe-e- _2-

Atoms of elements from the left side of the periodic table will lose electrons.

When an atom loses an electron it has more protons than electrons, so it is a positively charged ion.

Sodium will lose one electron to create a sodium ion with a “plus one” charge

Na

e-

+

A Magnesium atom will lose two electrons to form an ion with a charge of positive two.

Mg

e-

+

e-

2+

The energy required to remove an electron from an atom is called ionization energy.

First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period.

Across a period left to right

Atoms get smaller, so it is more difficult to remove tightly held electrons.

Down a group

Atoms get bigger so outer electrons are easier to remove.

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

Electronegativity values decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period.

Explanation of the electronegativity trend is also related to atomic size.

The smaller the atom the better it can attract electrons because they are closer to the positive nucleus.