Atoms and Elements. Goals: Describe atomic structure and define atomic number and mass number. Understand the nature of isotopes and calculate atomic weight from the isotopic masses and abundances. Explain the concept of the mole and use molar mass in calculations.
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Describe atomic structure and define atomic number and mass number.
Understand the nature of isotopes and calculate atomic weight from the isotopic masses and abundances.
Explain the concept of the mole and use molar mass in calculations.
Know the terminology of the periodic table.
- Rays emitted by polonium and radium – radioactive atoms disintegrate and emit rays: alpha (a), beta (b), gamma (g).
**Contradicted Dalton’s postulate: “atoms are indivisible”.
Same charge-to-mass ratio detected for different elements: electrons are present in all atoms.
Millikan (charge of the electron), Goldstein (positive ions).
Atomic weightWhat is the mass number of an iron atom with 30 neutrons?
Average mass = ATOMIC WEIGHT
Boron is 19.9% 10B and 80.1% 11B. That is, 11B is 80.1 percent abundant on earth.
1 proton and 0 neutrons, protium
1 proton and 1 neutron, deuterium
1 proton and 2 neutrons, tritium
Gallium has two isotopes: 69Ga and 71Ga.How many protons and neutrons are in the nuclei of each of these isotopes? If the abundance of 69Ga is 60.1%, what is the abundance of 71Ga?
Students should become familiar with the
use of atomic number and mass number,
especially in isotopes calculations.
By changing the magnetic field, a beam of charged particles of different mass can be focused on the detector, and a spectrum of masses is observed.
Copper exists as two isotopes: 63Cu (62.9298 u) and 65Cu (64.9278 u). What is the approximate percentage of 63Cu in samples of this element?
you name wyzzlebium (Wz). The average atomic mass of Wz was found to be 303.001 amu and its atomic number is 120.
A) If the masses of the two isotopes of Wz are 300.9326 amu and 303.9303 amu, what is the relative abundance of each isotope?
B) What are the isotopic notations of the two isotopes? (e.g. W).
C) How many neutrons are in one atom of the more abundant isotope?
Mg burns in air (O2) to produce white magnesium oxide, MgO.
Students should become familiar with the organization of elements in the periodic table.
solutions (except Be).
Al resists corrosion (in HNO3).
Gallium can be a liquid at room temp.
b) 9 g of Na or 0.5 mol of Na
White and red P
1 dozen = 12 objects
Eggs are measured by the dozen
1 ream = 500 objects
Paper is measured by the ream, 500 sheets
Chemistry is a quantitative science—we need a “counting unit.”
Definition: 1 MOLE is the amount of substance that contains as many particles (atoms, molecules) as there are in __________________.
6.02214199 x 1023
1 mole = 6.022 x 1023 items
1 mol of 12C = 12.00 g of C = 6.022 x 1023 atoms of C
12.00 g of 12C is its MOLAR MASS
Taking into account all of the isotopes of C, the molar mass of C is 12.011 g/mol.
1 molar mass = atomic mass of an element in grams
1 mol of atoms = 6.022 x 1023 atoms
You can use these relationships to make conversions between number of atoms, mass, and moles.
It is essential to convert from moles to mass and from mass to moles.
Atomic weightWhat amount of Mg in moles is represented by 0.200 g? How many atoms?
Mg has a molar mass of 24.3050 g/mol.
Students should become familiar with calculations using molar mass and avogadro’s number.