Warm-up• Which of the following is not found in the

nucleus of an atom? A. Protons

B. Neutron

C. Electron

• What is the mass of each of the subatomic particles?

– Proton – 1 amu– Neutron – 1 amu– Electron – 0 amu

3-7 Representative Groups• Relate the number of valence electrons to

the groups in the periodic table and to properties of elements in those groups.

• Predict the reactivity of some elements based on their locations in the periodic table.

• Identify some properties of common representative (A group) elements

Groups• Alkali Metals

– Group 1 – 1 valence electron– Extremely reactive– Found in nature only in compounds.– Reactivity increase from top to bottom.

• Alkaline Earth Metals– Group 2– Two valence electrons.– Higher melting points than group 1.– Lower reactivity than group 1.

• Boron Family - Group 13– 3 valance electrons

• Carbon Family – Group 14– 4 valance electrons

• Nitrogen Family – Group 15– 5 valence electrons

• Oxygen Family – Group 16– 6 valance electrons

• Halogens– Group 17– 7 Valance electrons– Salt formers– Very reactive– Reactivity decreases top to bottom.

• Nobel Gases– Group 18– 8 valance electrons– Very stable– Almost no compound form with Nobel gases– Colorless, odorless gases

Element you might know• Sodium

– Alkali metal– Found in table salt – sodium chloride

• Magnesium– Alkali earth metal– Key to chlorophyll, which is need for plant to

make food.– Used to make steel stronger, but lighter.

• Calcium– Needed to keep strong bones and teeth– Main ingredient in chalk, toothpaste, and

pearls.

• Aluminum– Most abundant metal found in Earth’s crust.– Low re activity– Strong, lightweight, malleable and conductive.

• Carbon– All living organisms are built on carbon-based

compounds.

• Nitrogen– About 78% of earth’s atmosphere is nitrogen.– Used in fertilizers

• Oxygen – Most abundant element in earth’s crust.– Oxygen is highly flammable.– Ozone is another form of oxygen that is found

in the upper atmosphere, which absorbs harmful radiation.

• Fluorine– Used in toothpaste to help prevent tooth

decay.– Used in nonstick coatings

• Chlorine

– Used chorine bleach– Added to city water supplies and pools to kill

bacteria.

• Argon– Highly unreactive element– Used in light bulbs to increase lifetime.– Used in “neon” lights – lavender color.

3-7 Summary• What do elements in the same group have

in common?– Similar properties– Same number of valence electrons.

• How many valence electrons to group 1 have? What are properties? Name?– Alkali metals– Extremely reactive– 1 valence electron– Reactivity increases top to bottom.

3-8 Summary (Cont.)• How can one tell the difference between

group 1 and 2?– Reactivity with water, Alkali earth metals are

less reactive.

• What do halogens have in common?– 7 valence electron. – Very reactive nonmetals

• Describe the characteristics of Nobel gases.– Colorless, odorless, completely unreactive

gases.