Chemistry Term 2 Review

Atomic Structure The nucleus is very dense and small. Contains protons (positively charged with a mass of 1 amu: atomic mass unit) Contains neutrons (neutral, mass of 1 amu; add only to the mass of the atom) The charge of the nucleus is positive due to the charge of the protons. Atomic number is the number of protons Mass number is the number of protons AND neutrons.

Atomic Structure Surrounding the nucleus is the electron cloud, which is most of the volume of the atom and is mostly empty space. Contains the electrons, which are negatively charged and a mass that is 1/1840 that of a proton. The physical and chemical properties of an element are determined by the electrons.

Calculating Protons, Electrons, Neutrons Using the periodic table: –Atomic number is the number of protons –In neutral atoms, # of protons = # of electrons, therefore, the atomic number is also the number of electrons. –To find number of neutrons: Subtract the atomic number (smaller number) from the mass number (atomic mass rounded to a whole number)

Isotopes The atomic mass is the WEIGHTED average of all an element’s isotopes. Isotopes of the same element vary ONLY IN NUMBER OF NEUTRONS. Two isotopes of the same element will have the same number of protons, electrons, atomic number, atomic masses (the average), but will have different MASS NUMBERS.

Famous Scientists Thomson: Plum Pudding Model Nucleus discovered by Rutherford (Gold Foil Experiment) Bohr: Orbital Model

Quantum Model: Current Model

Order of level by energy: (low to high) –s, p, d, f –S has one orbital (2 electrons max) –P has three orbitals (6 electrons max) –D has five orbitals (10 electrons max) –F has seven orbitals (14 electrons max)

s, p, d, f blocks of periodic table

Valence Electrons Electrons in the outermost energy level Maximum number is 8, in order to meet the OCTET RULE (makes them stable like a noble gas) Valence electrons are shown in Lewis dot diagrams. Representative groups (group A): Group number is the number of valence electrons.

Orbital Diagrams Show electrons as arrows. One up arrow and one down is an electron pair. In multiple orbitals (like in p, d, or f): all the up arrows go in first and then the down arrows pair with them (“seats on the bus”)

Which is correct for Carbon?

Determining Electrons in an Energy Level Reminder: If n=the energy level, then the maximum number of electrons that can be found in that level (total) is 2n 2. Example: The maximum number of electrons in the second energy level (n=2) is 2(2) 2 = 8 and this makes sense, because the second energy level has the orbitals: 2s 2 and 2p 6 …8 electrons total.

Electron Configuration Electron configuration is the pathway into which electrons fall as they are arranged in the atom. The arrow diagram shows the order in which the levels and orbitals are filled:

Electron Configuration Examples

Areas of the Periodic Table Vertical Columns: Groups Horizontal Rows: Periods Alkali metals Alkaline Earth Metals Transition metal Inner Transition metals Metalloids Nonmetals Halogens Noble Gases

Name this Element Group 4A, period 2 Group 7A, period 5 Lightest noble gas Has the noble gas configuration:(Ne)3s 2 3p 2 Heaviest Alkali metal Is larger than chlorine, smaller than iron, and has 2 valence electrons.

Periodic Table Facts: Metals The majority of elements are metals. Metalloids (along the stair-step line) have properties of both metals and nonmetals Transition elements are columns Alkali metals (1A) are very reactive metals Alkaline Earth metals are in group (2A).

Periodic Table Facts: Nonmetals Common Nonmetals: H, C, O, N, S, P Halogens (7A) are very reactive nonmetals Noble gases (8A) are unreactive (inert, stable) because their outer energy level is filled and meets the octet rule. Nobel gas configuration: (ns 2 np 6 n=outermost energy level)

Types of Radiation Alpha particles: 2+ charge, least penetrating. Beta particles: 1- charge Gamma Rays: 0 charge, most penetrating.