Unit 2: Atoms and the Periodic Table
Atoms and the Periodic Table
Overview
This unit covers the concepts related to atoms and the organization of elements in the periodic table.
The Periodic Table
Demetri Mendeleev: Credited for creating the first version of the modern periodic table.
Structure: Elements are arranged in columns (groups) that exhibit similar chemical properties.
Elements are listed in order of increasing atomic number.
Groups of Elements
Three Main Groups:
Metals: Located on the left side of the table (except for hydrogen).
Nonmetals: Located on the right side.
Metalloids: Found along the stair-step line on the periodic table (exception: Aluminum).
Stair-step Line: Begins under Boron.
Physical Properties of Metals
Metals comprise over 80% of all elements.
Conductive Properties:
Efficient conductors of heat and electricity.
Malleability: Can be hammered into thin sheets.
Ductility: Can be drawn into wires.
Lustrous appearance (shiny).
Tend to lose electrons during chemical reactions.
All metals (besides mercury) are solid at room temperature; they have high melting and boiling points.
Categories of metals: Alkali, alkaline earth, transition, and inner transition metals.
Physical Properties of Nonmetals
Nonmetals are found on the right side of the periodic table.
Key Characteristics:
Poor conductors of electricity and heat.
Exist as solids, liquids, and gases; bromine is the only liquid nonmetal at room temperature.
Not ductile or malleable; tend to be brittle.
Lack luster with lower melting and boiling points.
Tend to gain electrons in chemical reactions.
Physical Properties of Metalloids
Location: Found along the stair-step line.
Possess properties of both metals and nonmetals.
Exhibit various melting and boiling points.
Act as semi-conductors of electricity.
Some metalloids may have luster, but they are generally more brittle than metals and less brittle than nonmetals.
Periodic Families
Elements categorized into groups (families) based on shared properties:
Group 1 (1A): Alkali Metals
Group 2 (2A): Alkaline Earth Metals
Group 13 (3A): Boron Group
Group 14 (4A): Carbon Group
Group 15 (5A): Nitrogen Group
Group 16 (6A): Chalogens (Oxygen group)
Group 17 (7A): Halogens
Groups 3-12: Transition Metals
Group 18 (8A): Noble Gases
Lanthanides and Actinides: Inner transition elements.
Arrangement of Elements
Elements organized vertically into groups (families) and horizontally into periods.
Example of elements: Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), Radium (Ra).
Valence Electrons
Atoms in the same family have the same number of electrons in their outermost shell, known as valence electrons.
These electrons are involved in chemical reactions, explaining why elements in the same family exhibit similar properties.
Group 2 Atom Characteristics
Group 2 atoms have 2 electrons in their outer shells:
Beryllium (Be): Atom.
Magnesium (Mg): Atom.
Bonding and Properties
The number of valence electrons affects how an atom bonds, influencing the element's chemical properties. Elements in the same group have similar bonding behaviors.
Valence Electrons by Family
The number of valence electrons in families is:
Family 1: 1
Family 2: 2
Family 13: 3
Family 14: 4
Family 15: 5
Family 16: 6
Family 17: 7
Family 18: 8
Atoms Per Period
Each row (period) of the periodic table has the same number of energy levels.
Period 4 Atoms
Atoms in period 4 possess 4 electron-containing shells or energy levels:
Examples include Potassium (K), Iron (Fe), and Krypton (Kr).
Group Analysis
Group 1A (Alkali Metals) is highly reactive as they possess only one valence electron.
Reactivity of Alkali Metals
Demonstrated their high reactivity by their reaction with water.
Group 2 Properties
Deposited Alkaline Earth Metals are fairly reactive and are found predominantly in earth's crust.
Transition Metals
Characteristics:
Malleable (can be bent/hammered).
Good electrical conductivity.
Less reactive than other metals.
Real-world Context
Identify various items that contain transition metals.
Metalloids
Located adjacent to the stair-step line.
Share properties with both metals and nonmetals; significant semi-conductors include Silicon (Si) and Germanium (Ge).
Applications of Semiconductors
Importance of understanding where semiconductors are used in technology.
Halogens
Located in group 17; highly reactive nonmetals.
Notable for their poisonous nature.
Insight on Chlorine
Historically used as a chemical weapon in WWI and by the Nazis in WWII.
Noble Gases
Inert gases known for being unreactive due to filled electron shells.
Used in specialized applications like lighting.
Inner Transition Metals
Comprised of Lanthanides and Actinides known for being heavy and often radioactive.
Dalton's Atomic Theory
Fundamental principles regarding the nature of atoms and elements:
All elements consist of atoms.
Atoms of the same element are identical and distinct from other elements.
Compounds are formed from different elements' atoms.
Atoms are conserved in chemical reactions.
Parts of an Atom
Nucleus: Contains protons and neutrons, holding most of the atom's mass.
Electron Cloud: Area surrounding the nucleus containing electrons organized into energy levels.
Atomic Structure
Subatomic Particles:
Protons: Positive charge, located in the nucleus; identifies the element.
Neutrons: Neutral charge, also in the nucleus.
Electrons: Negative charge, found in the electron cloud.
Atomic Mass Units
Mass of Subatomic Particles:
Proton: 1 amu
Neutron: 1 amu
Electron: negligible mass (0 amu).
Understanding Atomic Number
The atomic number signifies the number of protons and thus identifies the element.
Relates directly to the number of electrons in a neutral atom.
Determines charge, neutrons, and mass number.Practice Problems
Questions to reinforce comprehension of atomic structure and properties.
Periodic Table Elements
Elements represented by atomic number, symbol, and average atomic mass.
Average Atomic Mass Calculation
Elementary example calculations explained:
Abundance impacts average atomic mass.
Isotopes
Definition: Atoms with the same number of protons but different numbers of neutrons define isotopes.
Isotope Notation
Understanding nuclear symbols, including mass number and charge notation examples.
Diatomic Molecules
Atoms of the same element bonded together; significant for knowing the 7 major diatomic molecules.
Average Atomic Mass Overview
Discusses how to compute the average atomic mass based on isotopes and their abundances.
Summary of Applications
Importance of knowing average atomic mass in chemistry and periodic table application.
Charges by Family
Overview of typical charges for ions in groups for easy reference.
Practice Problems for Ions
Exercises on determining ion charges and their relation to electron transfer.
Lewis Structures
Representation of an element and its valence electrons, aiding in visualizing bonding.
Drawing Lewis Structures
Step-by-step process for creating Lewis structures focusing on valence electrons.
Understanding Ions
Dissects cations and anions, emphasizing metal and nonmetal behavior in electrons.
Polyatomic Ions
Definition: Groups of atoms that collectively act as a single charged unit.
Common Polyatomic Ions List
List and definitions of common polyatomic ions for reference:
Examples such as ammonium, sulfate, and nitrate.
Isotopes Summary
Clear definition and distinction between isotopes, mass number, and element identification.
Average Atomic Mass Calculation Examples
Step-by-step numeric examples demonstrating average mass calculations.
Further Practice Problems
Additional problems for cementing understanding of isotopes and average atomic mass calculations.
Historical Contributions to Atomic Theory
Contributions from various scientists to the understanding of atomic structure, including Democritus, Dalton, and Rutherford.