Chapter 2: Elements and the Periodic Table

Chapter 2: Elements and the Periodic Table

2.1 Elements

  • Definition of an Element:

    • An element is a pure substance that cannot be broken down into simpler substances by a chemical reaction.

    • Each element is identified by a one- or two-letter symbol.

    • Elements are arranged in the periodic table, and their position reveals much about their chemical properties.

2.1 Elements: Common Elements and Their Symbols

  • Table 2.1: Common Elements and Their Symbols

    • Examples include:

    • Bromine (Br)

    • Calcium (Ca)

    • Carbon (C)

    • Chlorine (Cl)

    • Chromium (Cr)

    • Cobalt (Co)

    • Copper (Cu)

    • Fluorine (F)

    • Hydrogen (H)

    • Iodine (I)

    • Lead (Pb)

    • Magnesium (Mg)

    • Manganese (Mn)

    • Molybdenum (Mo)

    • Nitrogen (N)

    • Oxygen (O)

    • Phosphorus (P)

    • Potassium (K)

    • Sodium (Na)

    • Sulfur (S)

    • Zinc (Zn)

2.1A Elements and the Periodic Table

  • The periodic table divides elements into three groups:

    • Metals:

    • Located on the left side of the periodic table.

    • Properties:

      • Good conductors of heat and electricity.

      • Shiny solids at room temperature (except mercury, which is liquid).

    • Nonmetals:

    • Located on the right side of the periodic table.

    • Properties:

      • Dull appearance.

      • Usually poor conductors of heat and electricity.

      • Can be solids (sulfur, carbon), liquids (bromine), or gases (nitrogen, oxygen).

    • Metalloids:

    • Located on the stair-step line starting at boron (B) to astatine (At).

    • Properties: Intermediate between metals and nonmetals.

    • Seven metalloids include:

      • Boron (B)

      • Silicon (Si)

      • Germanium (Ge)

      • Arsenic (As)

      • Antimony (Sb)

      • Tellurium (Te)

      • Astatine (At)

2.1B Focus on the Human Body

  • Building-Block Elements:

    • Four elements making up 96% of the mass of the human body:

    • Oxygen (O)

    • Carbon (C)

    • Hydrogen (H)

    • Nitrogen (N)

    • Carbon, hydrogen, and oxygen are vital for biological molecules (proteins, carbohydrates, lipids, nucleic acids).

    • Proteins and nucleic acids incorporate nitrogen.

  • Major Minerals:

    • Required in daily diet (minimum 100 mg each).

    • Examples include Magnesium (Mg) and Sulfur (S) (found in proteins).

  • Trace Elements:

    • Needed in amounts usually less than 15 mg.

    • Iodine (I) is critical for thyroid function.

2.1C Compounds

  • Definition of a Compound:

    • A compound is a pure substance formed by chemically combining two or more elements together.

  • Chemical Formula Components:

    • Includes element symbols indicating identity and subscripts showing atom ratio.

    • Example:

      • Water (H2O): 2 Hydrogen atoms, 1 Oxygen atom.

      • Propane (C3H8): 3 Carbon atoms, 8 Hydrogen atoms.

2.2 Structure of the Atom

  • Basic Concept:

    • All matter comprises atoms, which are composed of three subatomic particles.

Table 2.3: Properties of Subatomic Particles

  • Protons:

    • Charge: +1

    • Mass: 1.6726 imes 10^{-24} g or 1 amu

  • Neutrons:

    • Charge: 0

    • Mass: 1.6749 imes 10^{-24} g or 1 amu

  • Electrons:

    • Charge: -1

    • Mass: Negligible ext{approximately } 9.1094 imes 10^{-28} g

Atomic Structure

  • Nucleus:

    • Contains protons and neutrons, dense core of the atom, location of most of the atom’s mass.

  • Electron Cloud:

    • Contains electrons and comprises the majority of the atom’s volume, primarily empty space.

  • Electromagnetic Interaction:

    • Opposite charges attract while like charges repel:

    • Protons and electrons attract each other.

    • Electrons repel other electrons.

Atomic Number (Z)

  • The atomic number is the number of protons in the nucleus.

    • A neutral atom has equal numbers of protons and electrons, hence Z equals both.

2.3 Isotopes

  • Definition of Isotopes:

    • Atoms of the same element with a different number of neutrons.

  • Isotope Notation:

    • Represented with atomic number as a subscript and mass number as a superscript.

    • Mass number = Number of protons + Number of neutrons.

Example: Chlorine Isotopes

  • Chlorine-35:

    • ^{35}_{17}Cl

  • Chlorine-37:

    • ^{37}_{17}Cl

Other Examples of Isotopes

  • Hydrogen Isotopes:

    • Protium: ^{1}_{1}H (1 proton)

    • Deuterium: ^{2}_{1}H (1 proton, 1 neutron)

    • Tritium: ^{3}_{1}H (1 proton, 2 neutrons)

2.3B Atomic Weight

  • Definition:

    • The atomic weight is the weighted average of the masses of the naturally occurring isotopes of a particular element, reported in atomic mass units (amu).

2.4A Basic Features of the Periodic Table

  • Periodic Table Layout:

    • Rows are called periods; columns are called groups.

    • Main Group Elements:

    • Tall columns on the right and left; groups numbered 1A to 8A.

    • Transition Metal Elements:

    • 10 short columns in the center; groups numbered 1B to 8B.

    • Inner Transition Elements:

    • Includes lanthanides and actinides; no group numbers assigned.

2.4B Characteristics of Groups 1A, 2A, 7A, and 8A

  • Group 1A (Alkali Metals):

    • Elements include Li, Na, K, Rb, Cs, Fr.

    • Properties:

    • Soft, shiny, low melting points, good conductors of heat and electricity, react with water to form basic solutions.

  • Group 2A (Alkaline Earth Metals):

    • Elements include Be, Mg, Ca, Sr, Ba, Ra.

    • Properties:

    • Shiny solids, less reactive than alkali metals.

  • Group 7A (Halogens):

    • Elements include F, Cl, Br, I.

    • Properties:

    • Exist as diatomic molecules, reactive with many elements; classified as gases (F, Cl), liquid (Br), and solid (I).

  • Group 8A (Noble Gases):

    • Elements include He, Ne, Ar, Kr, Xe, Rn.

    • Properties:

    • Stable atoms, rarely combine with other elements to form compounds.

2.7 Valence Electrons

  • Definition:

    • Electrons in the outermost shell of an atom.

  • Relation to Group Number:

    • Elements in the same group possess the same number of valence electrons and similar electronic configurations.

    • The group number (1A–8A) corresponds to the number of valence electrons for main group elements (except Helium).

  • Importance:

    • Similar electronic configurations lead to similar chemical properties among elements of the same group.