[LEC]

• What is the study of chemistry primarily concerned with?

  Chemistry is the study of matter and the changes it undergoes.
• What are the two main classifications of matter?

  • Pure substances
  • Mixtures
• What is a mixture?

  A mixture is a combination of two or more pure substances which is physically separable into pure substances.
• What distinguishes homogeneous matter from heterogeneous matter?

  Homogeneous matter has a uniform composition throughout, while heterogeneous matter has a nonuniform composition.
• What defines a pure substance?

  A pure substance has a fixed composition that cannot be further purified.
• How are elements and compounds different?

  Elements cannot be subdivided by chemical or physical means, while compounds are formed by the chemical combination of two or more elements in fixed ratios.
• What is a substance?

  A substance is a form of matter that has a definite composition and distinct properties.
• What are monoatomic elements? Give an example.

  Monoatomic elements consist of single atoms, such as Helium (He) and Neon (Ne).
• How many diatomic elements are there, and can you name a few?

  There are seven diatomic elements: H2, N2, O2, F2, Cl2, Br2, and I2.
• What are polyatomic elements? Provide an example.

  Polyatomic elements have three or more atoms per molecule, such as O3, P4, and S8.
• What is the definition of a compound?

  A compound is formed when two or more elements combine chemically in fixed ratios.
• What are the key points of John Dalton's Atomic Theory?

  1. All matter is composed of very tiny particles called atoms.
  2. All atoms of the same element have the same chemical properties.
  3. In a chemical reaction, no atom of any element disappears or changes into another element.
  4. Compounds are formed by the chemical combination of two or more atoms.
  5. Molecules are tightly bound combinations of two or more atoms that act as a single unit.
• Who discovered the Law of Conservation of Mass?

  Antoine Lavoisier discovered the Law of Conservation of Mass.
• What does the Law of Conservation of Mass state?

  It states that matter can be neither created nor destroyed.
• What is the Law of Constant Composition?

  The Law of Constant Composition states that any compound is always made up of elements in the same proportion by mass.
• What does the Law of Multiple Proportions describe?

  It describes that different compounds made up of the same element differ in the number of atoms of each kind that combine.
• What are atoms considered in chemistry?

  Atoms are considered the basic building blocks of matter.
• What is the unit of mass used in atomic mass units (amu)?

  One amu is defined as the mass of an atom of carbon with 6 protons and 6 neutrons in its nucleus.
• What is the value of 1 amu in grams?

  1 amu = $1.6605 \times 10^{-24} \text{ g}$
• What are the relative sizes of an atomic nucleus and an atom?

  • Thickness of A4 sheet: $10^{-3} \text{ m}$
  • Thickness of a cell membrane: $10^{-8} \text{ m}$
  • Thickness of a nucleus: $10^{-14} \text{ m}$
• What is the mass number (A) of an atom?

  The mass number (A) is the sum of the number of protons and neutrons in the nucleus of an atom.
• What is the atomic number (Z) of an atom?

  The atomic number (Z) is the number of protons in the nucleus of an atom.
• What are isotopes?

  Isotopes are atoms with the same number of protons but a different number of neutrons.
• How do you determine the number of protons, neutrons, and electrons in an atom? Provide examples.

  1. Identify the atomic number for protons.
  2. Subtract the atomic number from the mass number for neutrons.
  3. For neutral atoms, the number of electrons equals the number of protons.

  Examples:

  • For $^{17}_{8}O$: 8 protons, 9 neutrons, 8 electrons.
  • For $^{199}_{80}Hg$: 80 protons, 119 neutrons, 80 electrons.
• What is atomic weight?

  Atomic weight is the weighted average of the masses (in amu) of the naturally occurring isotopes of an element.
• How do you calculate the average atomic weight of an element with isotopes?

  Average atomic weight is calculated using the relative abundance and mass of each isotope.
• Calculate the average atomic weight of rhenium (Re) with isotopes.

  • Isotope ¹⁸⁷Re: 62.60% abundance, mass 186.956 amu.
  • Isotope ¹⁸⁵Re: 37.40% abundance, mass 184.953 amu.
  • Average atomic weight = $(0.6260 \times 186.956) +$$(0.3740 \times 184.953)$.
• Calculate the average atomic weight of lithium (Li) with isotopes.

  • Isotope ⁶Li: 7.42% abundance, mass 6.015 amu.
  • Isotope ⁷Li: 92.58% abundance, mass 7.016 amu.
  • Average atomic weight = $(0.0742 \times 6.015) +$$(0.9258 \times 7.016)$.
• What is the periodic table?

  The periodic table is a chart showing all the elements in columns with similar chemical properties.
• Who arranged the known elements in the periodic table?

  Dmitri Mendeleyev arranged the known elements in order of increasing atomic weight.
• What did Mendeleyev observe about the properties of elements?

  Mendeleyev observed that certain sets of properties recur periodically.
• How are electrons arranged in an atom?


  • Electrons are confined in specific regions called principal energy levels/shells (n = 1, 2, 3, ...).
  • The closer an electron is to the nucleus, the more strongly it is held and the harder it is to remove.
• What are subshells and how are they defined?


  • Subshells are divided into s, p, d, f.
  • The number of subshells is equal to the principal energy level (n).
• How many orbitals are in the s subshell, and how many electrons can it hold?

  The s subshell contains 1 orbital and can hold 2 electrons.
• How many orbitals are in the p subshell, and how many electrons can it hold?

  The p subshell contains 3 orbitals and can hold 6 electrons.
• How many orbitals are in the d subshell, and how many electrons can it hold?

  The d subshell contains 5 orbitals and can hold 10 electrons.
• How many orbitals are in the f subshell, and how many electrons can it hold?

  The f subshell contains 7 orbitals and can hold 14 electrons.
• What are degenerate orbitals?

  • Degenerate orbitals are orbitals that have the same energy.
  • Energy of an orbital is influenced by the size and shape of the orbital.
• What is electron configuration?

  • Electron configuration describes the orbitals that its electrons occupy.
  • It follows specific rules for filling orbitals.
• What are the rules of electron configuration?

  1. Aufbau Principle: Orbitals fill in the order of increasing energy.
  2. Pauli’s Exclusion Principle: Each orbital can hold up to two electrons with spins paired.
  3. Hund’s Rule: Each orbital of equal energy becomes half filled before any becomes completely filled.