# Essay on Study Guide

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Chapter 2- Study Guide
Mass number- this can be found by adding up the number of protons and neutrons in the nucleus.
Ex: Uranium 92+146=238mass number
Isotopes- Atoms that contain the same number of protons but different number of neutrons
Ex: Uranium-235has 143 neutrons & Uranium-238has 146 neutrons.
Atomic number = Protons
Atomic mass- atomic number = Neutrons
Nuclear Symbol

Atomic masses- Indicates how heavy on average one atom of that element is
EX: Mass of C-12 atom = 12 amu
Isotopic abundance- Atom %’s in nature
EX: On worksheet #3
Isotope
Atomic Mass
Abundance
Cl-35
34.97 amu
75.53%
Cl-37
36.97 amu
24.47%

Ex: Calculate the mass of an arsenic atom
74.92 g As
6.022 x 1023 atoms As 1 atom As x

Periods- Horizontal rows in the Periodic Table (Left to right)
Groups-Vertical Columns (up and down)
Molecular Formula’s- the number of atoms of each element is indicated by the subscript written after the symbol of the element.
Ex: H2O
Going from a structural formula to molecular: Combine all of your like elements together and add all of them up to get your subscripts
CH3CH2OH C2H6O
Ions- the charged particles when an atom gains or loses electrons.
EX: Na+ , Ca2+ , Cl- , O2-
Na+ has 10e- compared to Na which has 11e-
O2- has 10e- compared to O which has 8e-
Ionic compounds are held together by strong electrical forces between oppositely charged ions (ex. Na+ and Cl-). These are also known as Ionic Bonds. *(Remember transition metals you need to use roman numerals in your equations) Ex- Cr(NO3)3 Chromium(III)Nitrate ; CaS Calcium sulfide
Polyatomic ions
+1
-1
-2
-3
NH4+ (ammonium)
OH- (Hydroxide)
CO32- Carbonate
PO43- phosphate
Hg2+
NO3-(Nitrate)
SO42- Sulfate

ClO3-(Chlorate)
CrO42- Chromate

ClO4- (perchlorate)…