2.1–2.3: Properties of Atoms, Molecules, and Water

2.1 Properties of Atoms

  • Elements & Atoms

    • Elements are pure substances, each with one type of atom. They cannot be broken down chemically. ( C, H, O, N )

    • Atoms:( nguyên tử) basic units of matter, composed of protons, neutrons, and electrons.

  • Atomic Structure & Identity

    • Nucleus: dense center with protons
      —have mass—(positive charge) and neutrons (neutral).

    • Electrons: negatively charged, move in orbitals around the nucleus.

    • Atomic Number—số hiệu nguyên tử— (Z)=Number of protons, defines the element (e.g., hydrogen \text{Z}=1 , carbon \text{Z}=6 ).

    • In neutral atoms, protons = electrons.

    • Atomic Mass—khối lượng nguyên tử— determined by protons + neutrons

  • Isotopes & Ions

    • Isotopes—đồng vị—: atoms of the same element with same proton but different numbers of neutrons (e.g., ^{12} \text{C}, ^{13} \text{C}, ^{14} \text{C} ).

    • Ions: atoms that gain or lose electrons, becoming charged. Nhường hoặc cho electron

      • Cation: positively charged (loses electrons, e.g., \text{H}^+ ).

      • Anion: negatively charged (gains electrons).

  • Electron Arrangement & Octet Rule

    • Orbitals: regions where electrons are likely to be found (e.g., 1s, 2s, 2p).

      • Thứ tự sắp xếp các orbital theo năng lượng tăng dần: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, \dots

      • s - first shell, p- 2 shell → the different is the shape

        • 2 electron per orbital, and 1 per orbital until every orbital has 1 electron

    • Electron Shells: energy levels for orbitals.

      • First shell (1s) holds up to 2 electrons.

      • Subsequent shells can hold up to 8 electrons (octet rule).

    • Valence Electrons: Hoá trị

    • electrons in the outermost shell, determine chemical behavior and bonding.

    • Atoms tend to achieve very stable outer shell with 8 electrons (octet)

    • only it participate in chemical bond ( liên kết hoá học )

  • Periodic Table: Organizes elements by recurring chemical properties and increasing atomic number.

2.2 Molecules and Chemical Bonds

  • Molecule—phân tử—Groups of two or more atoms held together by chemical bonds.

  • Chemical Bonds: Attractions that hold atoms together in molecules

  • Covalent Bonds—liên kết cộng hoá trị—

    • Formed by sharing valence electrons between atoms. ( chia sẻ electron với nhau đạt trạng thái ổn định)

    • Stability: Atoms share electrons to complete their outer shells (octet rule )

  • Polar vs. Nonpolar Covalent Bonds— Nhóm nhỏ trong Covalent Bonds

    • Electronegativity—độ âm điện—: atom's attraction for shared electrons.—khả năng hút electron—

    • CH → low electronegavity

    • ON- high electronegavity

    • If it in the same group then it non-polar , EX: C-C, C-H, H-H

    • If they go different then it polar

    • Polar Covalent—liên kết hoá trị có cực— Unequal sharing of electrons due to electronegativity differences—nguyên tử nào hút mạnh hơn thì mang điện tích âm , yếu thì dương

    • Nonpolar Covalent—liên kết hoá trị ko cực—: Equal or nearly equal sharing of electrons. Less soluble in water.

    • Cách phân biệt giữa polar và nonpolar : là dựa vào electronegativity

    • Nếu gần bằng nhau → nonpolar

    • Nếu có sự chênh lệch lớn → polar

  • Ionic Bonds— liên kết ion—sự nhường hoặc nhận electron để trái dấu và hút nhau—fully stole

    • Formed by the transfer of electrons, creating oppositely charged ions.

    • Example: Sodium Chloride (NaCl) - Na loses electron ( \text{Na}^+ ), Cl gains electron ( \text{Cl}^- ).

    • Dissolution in Water (Hydration): Water molecules surround and separate ions due to their polarity.

  • Chemical Reactions: Involve breaking and forming of chemical bonds; atoms are conserved but rearrange (Reactants \rightarrow Products).

2.3 Water

  • Polarity & Solubility—Tính phân cực và khả năng hoà tan —

    • Water is a polar molecule due to polar covalent bonds and bent shape.

    • Hydrophilic—yêu nước—: "Water-loving" substances; polar molecules that dissolve in water.

    • Hydrophobic—kị nước—: "Water-fearing" substances; nonpolar molecules that avoid water

    • If it has H-bonds → always polar

  • Hydrogen Bonds—liên kết hydro—very weak

    • Weak electrostatic attraction between a hydrogen and another electronegative atom (e.g., O or N). —Nguyên tử Hydrogen (H) phải đã gắn trực tiếp với một nguyên tử có độ âm điện cao → thường là O, N, hoặc F.— they not sharing

  • pH and Proton Concentration

    • pH: A measure of proton ( \text{H}^+ ) concentration in solution.

      ^+]

    • Scale: 0-14 ; Neutral: pH = 7

    • Acids—pH<7— Release \text{H}^+ , proton donor , hydrogen without electron then —> only proton left

    • Bases—pH>7—: Accept \text{H}^+ $$

    Important from the slide that ask on test :

  • label C

How to tell it polar and non-polar activity:

  • Solid line → covalent bonds

  • Dot line → H-bonds

→ Polar , have H-bonds

→ Covalent bonds