Unit+4

UNIT FOUR MIDTERM REVIEW Types of measurements: Mole: base comparison of all types of elements amu: measurement of one element or atom grams: measurement of a mole of atoms

Avogardo's Number- The number of particles of one mole of a pure substance 6.022 x 10^23

Atomic mass is expressed in atomic mass units, or amu

you should use amu when measuring a single atom, but use grams when there is more than one atom

scientists use the percent of existence of isotopes multiplied by the mass all totaled to get the mass example: Si exists 92.21% of the time, giving a mass of 27.98 amu. 4.7% of the time, giving a mass of 28.98 amu. And 3.09% of the time with a mass of 29.97 amu. What is the average amu? answer: (0.9221 x 27.98) + (0.0470 x 28.98) + (0.0309 x 29.97) = 25.8 amu + 1.36 amu + .9261 amu = 28.09 amu

Characteristics of amu (atomic mass units): isotopes = 1 atom of an element sample Characteristics of grams (molar mass) : 6.022 x 10^23 atoms, represents the "g" of any element on the periodic table. Example: 15.99g O / 1 mol = 6.022 x 10^23 atoms O

Characteristics of moles: an equal comparison for all elements. 1 mol = 6.022 x 10^23 atoms, no matter what element We measure "g" to get to a mole An atom=a single element a molecule=multiple elements grouped

Trends in the periodic table: Atomic radius: It increases as one moves vertically down the periodic table, and decreases as one moves right across the periodic table.

Ionization energy: The energy required for removing an electron from an element. it decreases as one moves vertically down the periodic table. It also increases as one moves horizontally right across the periodic table.

Shielding effect: A decrease in the attraction of the other electron to the positively charged nucleus (valence electrons) It increases as one moves vertically down the periodic table. It also remains constant as you move right across the periodic table, because the electrons aren't being added to a new s energy level.

Electronegativity: This is how strong the bonds are within a compound. Decreases as you move down the periodic table, because the energy levels are growing, and it increases as you move right across the periodic table, because the protons are added to the nucleus allowing for more electrons. Flourine has the most EN of any element at 4.0 and Francium is the least at 0.7.

Electron Affinity: A measure of the energy change that occurs as an electron is added to an atom. It has the same trends as electronegativity for the same reasons.

Group 1A on the periodic table are alkali metals, other than hydrogen Group 2A on the periodic table are alkaline earth metals Group 3B, 4B, 5B, 6B, 7B, 8B, 1B, and 2B are all transition metals Group 8A are noble gases Group 7A are halogens The lanthanide series are the elements in the F1 orbital. An actinide series are the elements in the F2 orbital. Non Metals are boron, carbon, nitrogen, oxygen, silicon, phosphorus, sulfate, acetate, selenium, and tellurium The metals are aluminum, gallium, germanium, indium, tin, antimony, thallium, lead, bismuth, and polonium The 7 diatomic elements are= Hydrogen, nitrogen, oxygen, flourine, chlorine, iodine, and bromine.

Q: What is the attraction of oxygen, in the compound H2O2, for the electrons that belong to hydrogen called? A: Electronegativity This is because the electronegativity is how strong the bonds are within a compound.

Q: What is the change in energy that occurs as an electron is removed from an isolated atom called? A: Ionization Energy This is because the ionization energy is the amount of energy required for removing an electron from an element

Q: What is the change in energy that occurs as an isolated atom acquires an extra electron called? A: Electron affinity This is because the electron affinity is the energy change that occurs as an electron is added to an atom

Q: Chlorine has 2 naturally occurring isotopes. The relative abundance of rubidium-85 is 72.17% its atomic mass is 84.91 amu. The relative abundance of rubidium-87 is 27.83%; its atomic mass is 86.91 amu. Determine the average atomic mass of rubidium. A: (.7217x84.91) + (.2783 x 86.91) = 85.47 amu Because you multiply the percentages with the amu and add them up to get the average atomic mass.

Q: Calculate the average atomic mass for silicon if 92.21% of its atoms have a mass of 27.98, 4.70% have a mass of 28.98 amu, and 3.09% have a mass of 29.97 amu. A: (.9221 x 27.98) + (.047 x 28.98) + (.0309 x 29.97) = 28.088 amu Because you multiply the percentages with the amu and add them up to get the average atomic mass.

Q: Which family of elements contains the most highly reactive metals? A: Alkali Metals Alkali metals have only one valence electron making them very unstable because they are very willing to give up their electrons.

Q: Which family of elements contains the least reactive metals? A: Noble Gases The outer energy level of noble gases is completely filled with electrons, so they do not easily gain or lose electrons making them very stable.