Lesson 4.1 Atoms, Bonding, and the Periodic Table

Vocabulary –

Valence electron –

Electron dot diagram –

Chemical bond -

What determines an Element’s Chemistry?

How do atoms combine to form compounds? The answer has to do with electrons and energy levels.

The number of protons in a neutral atom equals the number of electrons. Electrons are found in different energy levels (cloud levels). Electrons at higher energy levels have higher amounts of energy.

The valence electrons of an atom are those electrons that have the highest energy. Valence electrons are involved in chemical bonding. The number of valence electrons in each atom helps determine the chemical properties of that element.

Electron Dot Diagram – includes the symbol for the element surrounded by dots. Each dot stands for one valence electron.

Different elements can have from 1 to 8 valence electrons. An electron dot diagram includes the symbol for the element surrounded by dots. Each dot stands for one valence electron.

Bonding – Atoms tend to be more stable if they have 8 valence electrons. Atoms of neon, argon, krypton, and xenon have 8 valence electrons, so they are nonreactive (stable). Helium is stable with 2 electrons.

Atoms tend to form bonds so that they have 8 valence electrons and become more stable. When atoms bond, valence electrons may be transferred from one atom to another, or they can be shared between the atoms.

Chemical bond – the force of attraction that holds atoms together as a result of the rearrangement of electrons between them.

The number of valence electrons increases from left to right across each period. Each period begins with an element that has 1 valence electron. Except for Helium, a given period ends with an element that has 8 valence electrons.

Group 1 elements have 1 valence electron

Group 2 elements have 2 valence electrons

Group 13 elements have 3 valence electrons

Group 14 elements have 4 valence electrons

(Elements in Groups 3-12 follow a slightly different pattern)

Noble Gases – Group 18 elements have 8 valence electrons (helium has 2) and are stable, meaning they are unlikely to gain or lose electrons, do not share electrons with other atoms, nor react with other elements. Scientist have been able to force some of them form compounds, however.

Metals – Metal atoms react by losing their valence electrons. The reactivity of a metal depends on how easily its atoms lose valence electrons. The reactivity of metals decreases from left to right across the periodic table.

Alkali metals are highly reactive. When they lose their 1 electron, they are left with a stable arrangement of 8 electrons (2 in lithium) in their highest energy level (which is one energy level lower than the 1 valence electron that was lost) Lithium atoms are left with a stable arrangement of 2 electrons.

Nonmetals – become stable when they gain or share enough electrons to have 8 valence electrons. (Hydrogen is left with a stable arrangement of 2 electrons)

The nonmetals usually combine with metals by gaining electrons.

They can also combine with metalloids and other nonmetals by sharing electrons.

Atoms of Group 17, the halogens, have 7 valence electrons. A gain of one or more electrons gives these atoms a stable 8 electrons, so the halogens react easily with other elements.

Metalloids – can either lose or share electrons when they combine with other elements.

Hydrogen – shares its electron when forming compounds with other nonmetals to obtain a stable arrangement of 2 electrons.