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Aim: How are elements within a group alike?. Do Now: Take out a calculator and reference tables How many groups are there in the periodic table of elements? How are the elements in group 1 similar to each other?. Answer to the Do Now.
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Aim: How are elements within a group alike? Do Now: Take out a calculator and reference tables How many groups are there in the periodic table of elements? How are the elements in group 1 similar to each other?
Answer to the Do Now • Elements in group 1 have the same number of valence electrons. • How many do they have? • What about the other groups?
How can we use that information? • The valence electrons determines an element’s chemical properties. Therefore, we can predict how the members of a group will behave. • Note however, that even though members of a group have the same number of valence electrons, there can be a change in the type of element from top to bottom. • Example: Elements in group 14. Carbon is a nonmetal. Silicon and germanium are metalloids, and tin and lead are metals. • Therefore what can we say about the metallic characteristics of elements as we consider them from top to bottom?
Hydrogen • Why is hydrogen unique among the elements? • Hydrogen is the only element that does not belong to a group. Hydrogen does not share the same physical or chemical properties of the elements in group 1. • Hydrogen can both gain and lose an electron. Therefore, it can have a +1 or -1 oxidation state. Hydrogen can also share its electrons to form covalent bonds.
Groups 1 and 2 • Group 1 – called the alkali metals. • Group 2 – called the alkaline earth metals. • Both groups show metallic characteristics. • Members of both groups easily lose their valence electrons. What does this mean about their ionization energies and electronegativities? • Members of both groups are never found in nature in their atomic state. They are always found in compounds and can be isolated by electrolysis (an electrical current must be passed through them). • In general, from top to bottom, reactivity increases. • Which group do you think would be more reactive?
Group 15 • Another group that ranges from nonmetal to metal. • Contains two elements that are important for life processes; Nitrogen and Phosphorous. • Nitrogen (N2) is found as a stable gas at room temperature. Why?
Group 16 • Elements in group 16 also start as nonmetal and progress to metal from top to bottom. • Contains the element oxygen which is important for many reasons. • Oxygen is a diatomic molecule at room temperature. What does that mean about its bonds? • The electronegativity of oxygen is… • The first ionization energy of oxygen is… • What does that mean about oxygen’s reactivity?
Group 17 • Also known as the halogens when they are in free state. When they gain an electron they become negative ions. What will their charge be? • The salts formed from the bonding of these elements are called halides. • Even though all the members of this group are nonmetals, the trend towards metallic characteristics is still seen in this group. • Example: Iodine is a solid with some luster at room temperature.
Group 17 • The halogens are the only group with all three states of matter at room temperature. Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. • Astatine is a radioactive element that is not found in large amounts in nature. • Members of this group have high electronegativities and ionization energies. What does this mean about their reactivity? • Members of this group are always found in their combined form in nature. • Fluorine can only be prepared from its compounds by electrolysis. The other halogens can be prepared by chemical means.
Group 18 • Also called the noble gases. • Do not combine to form diatomic molecules. Instead they exist as monatomic molecules. Why? • These elements are highly unreactive. However, because fluorine has such a high attraction for electrons, it can attract electrons from some of the noble gases. • Only argon and xenon have produced stable compounds.
Reactions between groups • In general, we can expect that groups 1 and 17 will react with each other as well as groups 2 and 17. • The general formula we can use to predict the compounds made are: • When group 1 combines with group 17, we can use the formula MX where M represents group 1 (metal) and X represents group 17. • Example: KCl or NaCl • When group 2 combines with group 17, we can use the formula MX2 where M represents group 2. • Example: CaCl2 or MgCl2
