Chapter 2B Chem 150

Isotopes

Isotopes of an element differ in the number of neutrons they contain.

Mass number

Isotopes are identified by their mass number, the sum of protons and neutrons.

Nuclear symbol

A nuclear symbol has the mass number as a superscript to the left, and the atomic number as a subscript to the left of the atomic symbol.

Neutrons calculation

The number of neutrons is calculated by subtracting the atomic number from the mass number.

Nuclear Symbol for Carbon-12

C-12 or carbon-12

Nuclear Symbol for Carbon-13

C-13 or carbon-13

Nuclear Symbol for Carbon-14

C-14 or carbon-14

Barium-131

Mass number: 131, Atomic number: 56, Number of protons: 56, Number of neutrons: 75.

Mercury-197

Mass number: 197, Atomic number: 80, Number of protons: 80, Number of neutrons: 117.

Chlorine-35

Mass: 34.97 amu, Natural abundance: 75.76%.

Chlorine-37

Mass: 36.97 amu, Natural abundance: 24.24%.

Atomic mass

The atomic mass of an element is a weighted average of the mass of all of its isotopes, according to their natural abundance.

Calcium-40

Most abundant isotope on Earth with a natural abundance of 96.95%.

Calcium-42

Isotope with the greatest number of neutrons.

Calcium-43

Natural abundance: 0.19%.

Calcium-44

Natural abundance: 2.09%.

Atomic mass of calcium

40.08 amu, determined by adding the masses of each isotope multiplied by their fractional abundances.

Group

In the periodic table, a column of elements is known as a group or family.

Main Group Elements

The main group elements are identified as groups 1A-8A.

Transition Elements

Transition elements are in the middle of the periodic table.

Alkali Metals

Common name for Group 1A elements.

Alkaline Earth Metals

Common name for Group 2A elements.

Halogens

Common name for Group 7A elements.

Noble Gases

Common name for Group 8A elements.

Group Properties

Elements within a group share similar physical and chemical properties, reflecting the periodicity of the periodic table.

Period

The periodic table contains seven rows, referred to as periods.

Period 1

Period 1 contains only two elements, hydrogen and helium.

Metalloids

The eight metalloids are elements along the border of the bold diagonal steps separating metals and nonmetals.

Hydrogen Exception

Hydrogen is a nonmetal that appears with the metals.

Aluminum Classification

Aluminum is a metal and not a metalloid even though it borders the steps.

Physical Properties of Metals

Metals are shiny, exist as solids, liquids, and gases at room temperature, are good conductors of electricity, and are flexible.

Physical Properties of Nonmetals

Nonmetals are dull, exist as solids at room temperature (except Hg, a liquid), are poor conductors of electricity, and are brittle, hard or soft.

Macronutrients

Macronutrients are required in our diet in quantities greater than 100 mg a day.

Micronutrients

Micronutrients are required in quantities less than 100 mg a day.

Building Block Elements

Biological molecules are composed of the building block elements: C, H, N, O, P, and S.

Arrangement of electrons

Determines physical and chemical properties of the elements.

Quantum mechanics

Electrons can have only certain allowed energy levels.

n

Symbol for allowed energy levels.

Maximum Number of Electrons for Each Energy Level

Calculated using the formula 2n².

Energy Level 1

Maximum number of electrons = 2.

Energy Level 2

Maximum number of electrons = 8.

Energy Level 3

Maximum number of electrons = 18.

Core Concept - Energy Levels

Electrons exist only in allowed energy levels, identified as n=1, n=2, n=3 …, with higher values representing greater energy and distance from the nucleus.

Core Concept - Electron Arrangement

Electron arrangement for elements with atomic numbers 1-18 is determined by filling the lowest energy levels first.

Valence electrons

Electrons in the highest energy level of an atom.

Periodicity

Repeating patterns found in the periodic table related to physical and chemical properties and electron arrangements.

Group 1A elements

Have one valence electron.

Group 2A elements

Have two valence electrons.

Groups 3A-7A

Have three to seven valence electrons.

Group 8A elements

Have eight valence electrons and a filled valence energy level.

Core Concept - Elements in the Same Group

Elements in the same group have the same number of valence electrons.

Energy level containing valence electrons

Corresponds to the period of the atom.

Atomic Number

The number of protons in the nucleus of an atom.

Atomic Symbol

One or two-letter abbreviation for an element.

Electron arrangement for Hydrogen

n = 1.

Electron arrangement for Helium

n = 1.

Electron arrangement for Lithium

n = 2.

Electron arrangement for Beryllium

n = 2.

Electron arrangement for Carbon

n = 4.

Electron arrangement for Nitrogen

n = 2, 5.

Electron arrangement for Oxygen

n = 6.