Chaap 4

Elements and Compounds

Hydroxyapatite Composition

Hydroxyapatite, Ca5(PO4)3OH, is a major compound found in human bones and teeth. Understanding its elemental composition is important for recognizing the role of minerals in biological systems.

• Key Elements: Calcium (Ca), Phosphorus (P), Oxygen (O), Hydrogen (H)

• Application: Used in dental and orthopedic materials due to its similarity to natural bone mineral.

Periodic Table Groups and Properties

Group 1A (Alkali Metals)

Group 1A elements, known as alkali metals, share several physical and chemical properties.

• Properties:

  • Shiny appearance

  • Good conductors of electricity

  • React vigorously with water

  • Are solids at room temperature (except for inferred context: some may be liquid under specific conditions)

• Exception: They are not liquids at room temperature.

Group 8A (Noble Gases)

Group 8A elements, or noble gases, are characterized by their lack of chemical reactivity and unique physical properties.

• Properties:

  • Unreactive and rarely found in combination with other elements

  • Gases at room temperature

  • Do not react vigorously with water

  • Not good conductors of electricity

Classification of Elements

Metals, Nonmetals, and Metalloids

Elements are classified based on their physical and chemical properties.

• Metals: Elements that are typically shiny, malleable, ductile, and good conductors of heat and electricity. Example: Phosphorus is not a metal; Strontium is a metal.

• Metalloids: Elements with properties intermediate between metals and nonmetals. Example: Silicon is a metalloid.

• Noble Gases: Helium is a noble gas; nitrogen, oxygen, chlorine, and silver are not.

Atomic Structure

Subatomic Particles

Atoms consist of three main subatomic particles: protons, neutrons, and electrons.

• Protons: Positively charged particles found in the nucleus.

• Neutrons: Neutral particles found in the nucleus.

• Electrons: Negatively charged particles found in orbitals around the nucleus.

Nucleus Composition

The nucleus of an atom contains all the protons and neutrons.

• Key Point: Electrons are not found in the nucleus.

Atomic Number and Mass Number

The atomic number and mass number are fundamental for identifying elements and isotopes.

• Atomic Number (Z): Number of protons in the nucleus of an atom.

• Mass Number (A): Total number of protons and neutrons in the nucleus.

Formulas:

• Atomic Number: $Z = \text{number of protons}$

• Mass Number: $A = \text{number of protons} + \text{number of neutrons}$

• Number of Neutrons: $\text{Number of Neutrons} = A - Z$

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons.

• Key Point: Isotopes have the same atomic number but different mass numbers.

• Example: $^{50}\text{Sn}$ (Tin-50) has 50 protons and 50 neutrons.

Element Symbols

Common Element Symbols

Each element is represented by a unique one- or two-letter symbol.

Element	Symbol
Mercury	Hg
Copper	Cu
Sulfur	S
Silver	Ag

Sample Calculations and Applications

Calculating Atomic Structure

Understanding how to calculate the number of subatomic particles is essential for chemistry.

• Example 1: Potassium atom with 20 neutrons: $A = Z + \text{neutrons} = 19 + 20 = 39$

• Example 2: Neutral atom with 30 protons and 34 neutrons: $A = 30 + 34 = 64$

• Number of electrons in a neutral atom: Equal to the number of protons.

Isotope Notation

Isotopes are represented as $^{A}\text{X}$, where X is the element symbol and A is the mass number.

• Example: $^{50}\text{Sn}$ has 50 protons and 50 neutrons.

Summary Table: Atomic Structure Relationships

Term	Definition	Formula
Atomic Number (Z)	Number of protons	$Z$
Mass Number (A)	Protons + Neutrons	$A = Z + N$
Number of Neutrons (N)	Mass Number - Atomic Number	$N = A - Z$
Number of Electrons	Equal to protons in neutral atom	$E = Z$

Additional info:

• Some questions reference "Global Outcomes" and "Learning Obj." which are likely course objectives for skill development in chemistry.

• All content is foundational for GOB Chemistry, covering elements, atomic structure, periodic table, and basic calculations.