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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.