Holt Chapter 14 Chemical Bonding

Section 1 Electrons & Chemical Bonding

Chemical Bonding is the joining of atoms to form new substances. A chemical bond is a force of attraction that holds two atoms together.

A theory is a unifying explanation for a broad range of hypotheses and observations that have been supported by testing. Over the past 150 years, scientists have performed experiments that led to chemical bonding theories.

Valence electrons are the electrons in the outermost energy level of an atom. These electrons are used to form bonds.

Most atoms form bonds by gaining, losing, or sharing electrons until they have 8 valence electrons. Atoms of Hydrogen (H), Lithium (Li), and Helium (He) need only 2 electrons to fill their outermost level.

To understand how atoms form chemical bonds, you first need to determine the valence electron number. Use the atomic number to determine this. Ex, Sodium, 11 electrons, has 2e- in inner level, 8e- in 2nd level, and 1e- in third level. So 1 valence electron.

Looking at the periodic table, Groups 1,2 have same number of valence electrons as the group number. For groups 13-18, subtract 10 from the group number, and that is how many valence electrons the atom has. (Ex Carbon, group 14, has 4 valence e-)

Now it gets a little more complicated For Groups 3-12, the transitional metals, this general rule does NOT apply. They usually have 1 or 2 valence e-.

Atoms bond to have a filled outermost level Atoms bond to have a filled outermost level. If that level is already full, such as the inert gases, Group 18, they are less likely to form new bonds. They are basically happy campers as themselves.

Neon is such an example. It has 10 electrons, so 2 in inner level, and 8 in outermost level. This is ‘full’ - so no real need to bond to gain, lose or share electrons.

Magnesium, with 12 electrons, has 2 in innermost level, 8 in the second level, and 2 in outermost level. Therefore, it could LOSE 2 electrons, ending up with 8 in outermost shell.

Question Which electrons in an atom are likely to have more energy, A) - those in levels close to the nucleus, or B) - those farther away? Answer - B) those farthest away away

Question Why do some atoms rarely bond?

Question Why do some atoms rarely bond? Answer: They have a filled outermost energy level with 8 electrons, which makes them very non-reactive. Examples include the group 18 inert gases.

Question Which electrons in an atom are likely to have more energy, - those in levels close to the nucleus, or - those farther away?