General, Organic, and Biological Chemistry - Atoms and Elements Study Notes

Chapter 4: Atoms and Elements

Elements and Their Properties

  • Elements

    • Pure substances from which all other things are built.

    • Cannot be broken down into simpler substances.

    • Listed on the inside front cover of the text.

Chemical Symbols

  • Chemical Symbols

    • Represent the names of the elements.

    • Consist of one to two letters and start with a capital letter.

One-Letter Symbols

  • C: carbon

  • N: nitrogen

  • F: fluorine

  • O: oxygen

  • H: hydrogen

  • Al: aluminum

  • Ca: calcium

  • Co: cobalt

  • Mg: magnesium

Two-Letter Symbols

  • Na: sodium

  • Ag: silver (argentum)

  • Au: gold (aurum)

  • Fe: iron (ferrum)

  • Hg: mercury (hydrargyrum)

  • Pb: lead (plumbum)

  • K: potassium (kalium)

  • Rb: rubidium

  • Sr: strontium

Names and Symbols of Some Common Elements (Table 4.2)

Name

Symbol

Name

Symbol

Aluminum

Al

Argon

Ar

Gold

Au

Phosphorus

P

Helium

He

Platinum

Pt

Hydrogen

H

Radium

Ra

Silver

Ag

Calcium

Ca

Lithium

Li

Sodium

Na

Carbon

C

Magnesium

Mg

Fluorine

F

Nitrogen

N

Zinc

Zn

Barium

Ba

Chlorine

Cl

Neon

Ne

Iodine

I

Uranium

U

Note: Names in parentheses are ancient Latin or Greek words from which the symbols are derived.

The Periodic Table

  • Periodic Table

    • Organizes 118 elements into groups with similar properties.

    • Arranges elements in order of increasing atomic mass.

Structure of the Periodic Table

  • Elements are arranged according to properties.

  • Groups

    • Contain elements with similar properties in vertical columns.

  • Periods

    • Are horizontal rows counted from top to bottom of the table (Periods 1−7).

Group Names

  • Group 1A: Alkali Metals

  • Group 2A: Alkaline Earth Metals

  • Groups 3A–7A: Representative Elements

  • Groups 3B–2B: Transition Elements

  • Group 8A: Noble Gases

Group Specifics

  • Group 1A (1): Alkali Metals

    • Lithium (Li)

    • Sodium (Na)

    • Potassium (K)

    • Rubidium (Rb)

    • Cesium (Cs)

  • Group 2A (2): Alkaline Earth Metals

    • Beryllium (Be)

    • Magnesium (Mg)

    • Calcium (Ca)

    • Strontium (Sr)

    • Barium (Ba)

    • Radium (Ra)

Note: Strontium provides the red color in fireworks.

  • Group 7A (17): Halogens

    • Fluorine (F)

    • Chlorine (Cl)

    • Bromine (Br)

    • Iodine (I)

  • Group 8A (18): Noble Gases

    • Typically do not react with other elements.

Metals, Nonmetals, and Metalloids

  • The heavy zigzag line separates metals and nonmetals.

    • Metals

    • Located to the left.

    • Shiny, ductile, and good conductors of heat and electricity.

    • Solid at room temperature (except for mercury, Hg which is liquid).

    • Nonmetals

    • Located on the right side.

    • Dull, brittle, poors conductors, and often good insulators.

    • Low densities and melting points.

    • Metalloids

    • Located along the heavy zigzag line (except for aluminum and oganesson).

    • Exhibit properties of metals and nonmetals.

    • Better conductors than nonmetals but not as good as metals.

    • Used as semiconductors and insulators, can be modified to function as conductors or insulators.

Chemistry Link to Health: Elements Essential to Health

  • 20 elements are essential for the well-being/survival of the human body.

    • 4 elements (O, C, H, N) make up 96% of body mass.

    • Most hydrogen and oxygen is found as water (55-60% of body mass).

  • Macrominerals (Ca, P, K, Cl, S, Na, Mg) involved in

    • Formation of bones and teeth.

    • Maintenance of heart and blood vessels.

    • Muscle contraction, nerve impulses, and acid–base balance of body fluids.

    • Regulation of cellular metabolism.

Atoms

  • An atom is the smallest particle of an element that retains the characteristics of that element. Example: Aluminum foil contains aluminum atoms.

Dalton’s Atomic Theory

  • Atoms are tiny particles of matter;

  • Atoms of an element are similar to each other and different from those of other elements.

  • Atoms of two or more different elements combine to form compounds.

  • Atoms are rearranged to form new combinations in a chemical reaction; they are never created or destroyed during a chemical reaction.

Subatomic Particles

  • An electron is the first discovered subatomic particle (discovered by J.J. Thomson via cathode ray tube experiments).

    • Cathode rays contain negatively charged particles with much smaller mass than the atom.

    • Thomson's “plum-pudding” model of the atom includes protons and electrons randomly distributed within a positively charged cloud.

Rutherford’s Gold Foil Experiment

  • Conducted by Rutherford aiming positively charged particles at gold atoms.

    • Most particles went straight through, occasionally deflected.

    • Conclusion: Atoms have a small, dense, positively charged nucleus (center) that deflects particles coming close.

Structure of the Atom

  • An atom consists of:

    • Nucleus: central part containing protons and neutrons, holding most of the mass of the atom.

    • Electrons: occupy a large space around the nucleus.

Subatomic Particles in an Atom

  • Protons: positive charge (+)

  • Electrons: negative charge (-)

  • Neutrons: neutral charge

Note: Like charges repel, opposite charges attract.

Mass of the Atom

  • Most mass contained in the nucleus from protons and neutrons. Electrons contribute to the large volume of the atom.

  • Chemists utilize the atomic mass unit (amu):

    • 1 amu = 1/12 of the mass of a Carbon-12 atom, containing 6 protons, 6 neutrons.

    • 1 amu = 1 Dalton (Da).

    • Electrons not usually included in atomic mass due to their negligible mass.

Atomic Number and Mass Number

  • Atomic Number (Z):

    • Specific whole number per element, equal to the number of protons.

    • Appears above the symbol of an element in the periodic table.

Mass Number

  • Represents the number of particles (protons + neutrons) in the nucleus; always a whole number; some examples:

    • H: atomic number = 1

    • C: atomic number = 6

    • Cu: atomic number = 29

Isotopes

  • Isotopes are atoms of the same element with different mass numbers (same protons, different neutrons).

  • Distinguished by their atomic symbols.

Atomic Mass

  • Atomic mass: average of all naturally occurring isotopes of an element; the number below the chemical symbol in the periodic table.

    • Example: Chlorine has atomic mass of 35.45 amu.

  • To calculate atomic mass:

    1. Use experimental percent abundance for each isotope.

    2. Multiply the percent abundance by the atomic mass of that isotope.

    3. Sum the total mass of all isotopes.

Energy Levels and Electron Configuration

  • Electron Energy Levels:

    • Electrons with the same energy grouped in the same energy level, assigned principal quantum numbers (n = 1, 2,…).

    • Electrons absorb energy to move to higher levels; released energy corresponds to the difference between levels.

Electron Sublevels and Maximum Electrons

  • Each energy level consists of one or more sublevels: s, p, d, and f.

  • Sublevel capacities:

    • s: 1 orbital, 2 electrons

    • p: 3 orbitals, 6 electrons

    • d: 5 orbitals, 10 electrons

    • f: 7 orbitals, 14 electrons

Electron Configurations

  • Indicates electron placement in an atom; fills from lowest to highest energy level.

  • Orbital diagrams and electron configuration notation used to describe.

  • Always represent previous electrons using noble gas notation.

Trends in Periodic Properties

  • Ionization energy: energy to remove an outer electron decreases down a group and increases across a period.

  • Metallic character: increases down a group and decreases across a period.

  • Atomic size increases down a group and decreases across a period.

Summary of Trends in Periodic Properties

  • Periodic Property:

    • Valence Electrons

    • Remains the same top to bottom within a period; increases left to right.

    • Atomic Size

    • Increases top to bottom, decreases left to right.

    • Ionization Energy

    • Decreases down a group, increases across a period.

    • Metallic Character

    • Increases down a group, decreases across a period.

Learning Checks

  • Identify elements, their configurations, and characteristics by utilizing the periodic table and provided examples.