Study Guide: Alkali Metals, Alkaline Earth Metals, and Hydrogen
Summary This study guide covers alkali metals, alkaline earth metals and their properties, hydrogen, and important concepts like valence electrons, atomic radius, element density, and atomic mass. It also explores trends in reactivity and provides connections to Bohr models.
Hydrogen: A Special Case · Hydrogen is in Group 1 because it has one valence electron like alkali metals. However, it is not a metal. · Hydrogen has the lowest density of all elements, with an atomic number of 1 Alkali Metals (Group 1) Elements: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs). (You do not need to memorize these) Key Properties: · They are in Group 1 · Valence Electrons: Each alkali metal has 1 valence electron · Atomic Radius: Increases as you move down the Group because the outermost electrons are farther from the nucleus · Density: Increases as you move down the group because more subatomic particles are packed into the same space in the nucleus and they become more dense · Reactivity: Increases as the atomic radius grows, making it easier to lose the single valence electron Alkaline Earth Metals (Group 2) Elements: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba). (You do not need to memorize these) Key Properties: · Valence Electrons: Each alkaline earth metal has 2 valence electrons · Atomic Radius: Increases down the group because the outermost electrons are farther from the nucleus · Density: Higher than alkali metals and increases down the Group because the nucleus becomes denser because the number of protons and neutrons (subatomic particles) in the nucleus increases · Reactivity: Increases as the atomic radius grows, making it easier to lose the two valence electrons.
Here is a table that compares the two categories: Comparison of Alkali Metals and Alkaline Earth Metals Feature Alkali Metals (Group 1) Alkaline Earth Metals (Group 2) Valence Electrons 1 valence electron 2 valence electrons Reactivity Highly reactive, increasing as you move down the group Reactive, but less so than alkali metals; reactivity increases down the group Hardness Soft, can be cut with a knife Harder than alkali metals Density Low density, some can float on water Higher density than alkali metals Melting Points Lower melting points Higher melting points than alkali metals Atomic Radius Larger atomic radius than alkaline earth metals in the same period Smaller atomic radius than alkali metals in the same period Reaction with Water React vigorously with water React with water more slowly than AMs Common Uses Batteries (e.g., lithium), table salt (sodium chloride) Building materials (e.g., calcium in cement), dietary supplements (magnesium) Appearance Shiny when freshly cut, tarnishes quickly in air Shiny but tarnishes more slowly in air
Valence Electrons and Trends Valence electrons are the outermost electrons in an atom and determine how it reacts with other elements. Trends in Groups: · Atomic Radius: Increases as you move down because electrons are farther from the nucleus · Density: Increases as more subatomic particles are packed into the nucleus · Reactivity: Increases because it is easier to lose valence electron · Trends in Periods: Reactivity, density, and atomic radius generally increase for metals as the period increases
Atomic Mass and Atomic Number Atomic mass is the weighted average of all isotopes of an element. If the atomic mass is greater than 2x the atomic number, the element has more isotopes with more neutrons (e.g., Carbon 12 vs Carbon 14). · In Carbon 14, how many protons are in the nucleus? How many neutrons are in the nucleus? If the atomic mass and atomic number are nearly equal, there are few isotopes
Bohr Models and Identification Using Bohr Models: Like we did in class using the Bohr models drawn on the counters in the back of the lab, (1) be able to identify an element by counting the number of protons and neutrons; (2) know if it is an alkali metal or an alkaline earth metal by looking at a periodic table; (3) know how many valence electrons there are. · Identify the element by Counting the Protons; they equal the atomic number (Z) · Count Electrons: They are equal to the number of protons in a neutral atom · Count Neutrons: An isotope has MORE neutrons than protons · Be able to use the periodic table to identify the element. Be able to identify if it is an isotope
Identifying Isotopes: An isotope has the same number of protons, but a different number of neutrons compared to the standard element. There are more neutrons than protons!
Vocabulary Valence Electrons: The electrons in the outermost shell of an atom Atomic Radius: The distance from the nucleus to the outermost electron Density: The amount of mass in a volume (The number of neutrons and protons in the nucleus) Reactivity: How easily an element reacts Atomic Mass: The weighted average mass of an element’s isotopes Isotope: An atom with the same number of protons but a different number of neutrons
Sample Questions
Why does density increase as you move down a group? A. The nucleus gets larger. B. The nucleus contains more subatomic particles packed into the same space. C. The valence electrons move closer to the nucleus. D. There are fewer protons and neutrons. Answer: B.
Which trend is true for metals as you move down a group? A. Reactivity and density decrease. B. Reactivity and density increase. C. Reactivity increases, but density decreases. D. Reactivity decreases, but density increases. Answer: B.
Explain why the density of elements increases as you move down a group. Answer: Density increases because more subatomic particles (protons and neutrons) are added to the nucleus, but the nucleus size does not change. This makes the nucleus denser.
State 2 properties of alkali metals and 2 properties of alkaline earth metals Answer: State any two proper