Unit 1: The Atom

Question 1

Question 2

Atomic Theory explains …

Answer 2

Explains law of

• Conservation of Matter
• Definite Proportions – elements combine in definite, fixed ratios
• Constant Composition – for all samples of compound, same element composition by mass
• Multiple Proportions – the same elements can combine in multiple different ratios to form different compounds

Question 3

Atomic Theory allows

Answer 3

Allows stoichiometry:

• composition stoichiometry – mass relations within a substance.
• reaction stoichiometry – mass relations between substances in a reaction.

Question 4

Composition of the atom

Answer 4

Protons

Neutrons

Electrons

Question 5

Are atoms usually postive negative or neutral?

What gives an atom its properties?

What are atoms Identified by?

Answer 5

Usually neutral; can buildup (static); try to equalize charge

Ratios of the three particles give atom its properties

ID by proton - unchanging

Question 6

Nuclear Theory

Answer 6

Matter not uniform

• Most mass, all + charge in central nucleus
• Mostly empty space – negative electrons dispersed
• Number of negative electrons = positive protons

Question 7

What comprises 99.9% of atom’s mass ?

Answer 7

Nucleus

Question 8

How many identifiable elements are there?

How many are synthetic?

Answer 8

118 Identifiable elements

20 synthetic

Question 9

Elemental Symbol

Answer 9

• one or two letter abbreviation used to represent an element
• Some first two letters - F, Ne, O, Si, C
• Some one or two letters not first – Zn, Cl
• Some ancient name
  
  • Au (aurum)
  • Pb (plumbum)
  • W (wolfram)
  • K (kalium)
  • Na (natrium)

Answer 10

Question 11

Atomic Number

Answer 11

the number of protons contained within an atom’s nucleus

Question 12

Mass number

Answer 12

the sum of the number of protons and neutrons contained within an atom’s nucleus.

Question 13

Write the nuclide symbol for each of the following elements:

An element with 6 protons, 6 neutrons and 6 electrons

An element with 9 protons, 10 neutrons and 9 electrons

An element with 20 protons, 21 neutrons and 20 electrons

Question 14

Ion

Answer 14

a charged atom

Question 15

Cation

Answer 15

an ion with positive charge

Question 16

Anion

Answer 16

an ion with negative charge

Question 17

Formula unit

Answer 17

the simplest whole number charge neutral ratio of atoms

Question 18

Describe each of the following ions as a cation or an anion.

• Ca²⁺
• Al³⁺
• F^-
• N^3-
• Li⁺

Question 19

Isotope

Answer 19

atoms of the same element that have a different number of neutrons.

Question 20

Isotopic natural abundance

Answer 20

the percentage of an element which is made up of a particular isotope

Question 21

Atomic mass unit (amu)

Answer 21

the mass of 1/12 the mass of a (_6^12)C atom

Question 22

Atomic mass (weight)

Answer 22

the weighted average mass of all naturally occurring isotopes of an element.

Question 23

Boron-10 has a mass of 10.012937 amu and a % isotopic composition of 19.9%; Boron-11 has a mass of 11.009305 amu and % isotopic composition of 80.1%. What is the atomic mass of Boron to four significant figures?

Answer 23

10.81 amu

Question 24

Chromium-50 has a mass of 49.946050 amu and a % isotopic composition of 4.345%; Chromium-52 has a mass of 51.940512 amu and % isotopic composition of 83.789%; Chromium-53 has a mass of 52.940654 amu and % isotopic composition of 9.501%; Chromium-54 has a mass of 53.938885 amu and % isotopic composition of 2.365%. What is the atomic mass of Boron to five significant figures?

Answer 24

51.996 amu