Chemistry Notes - Atoms, Bonds, and Water PDF

Matter, Atoms, and Elements ​ Matter: Anything that has mass and takes up space. All matter is made of atoms. ​ Element: A substance consisting of only one kind of atom (e.g., hydrogen, carbon, oxygen). ​ Atom Structure: ○​ Protons: Positively charged, located in the n...

Matter, Atoms, and Elements ​ Matter: Anything that has mass and takes up space. All matter is made of atoms. ​ Element: A substance consisting of only one kind of atom (e.g., hydrogen, carbon, oxygen). ​ Atom Structure: ○​ Protons: Positively charged, located in the nucleus. ○​ Neutrons: Neutral, located in the nucleus. ○​ Electrons: Negatively charged, orbit the nucleus in electron shells. ​ Atomic Number: The number of protons in an atom (defines the element). ​ Isotopes: Atoms of the same element with different numbers of neutrons (e.g., Carbon-12 vs. Carbon-14). 2. Chemical Bonds ​ Covalent Bonds: Atoms share electrons (strong bond). ○​ Polar Covalent Bond: Electrons are shared unequally (e.g., water). ○​ Nonpolar Covalent Bond: Electrons are shared equally. ​ Ionic Bonds: One atom takes an electron from another, creating ions (charged atoms). ○​ Cations: Positively charged ions. ○​ Anions: Negatively charged ions. ​ Hydrogen Bonds: Weak bonds between a hydrogen atom and an electronegative atom (e.g., N, O, F). ​ Van der Waals Interactions: Very weak attractions between oppositely charged atoms. 3. Water and Its Properties ​ Polarity: Water is a polar molecule due to unequal sharing of electrons between oxygen and hydrogen. ​ Hydrogen Bonding: Water molecules form hydrogen bonds, giving water unique properties: ○​ Cohesion: Water molecules stick to each other (e.g., surface tension). ○​ Adhesion: Water molecules stick to other substances (e.g., water climbing up a plant stem). ○​ High Specific Heat: Water resists temperature changes, making it a good habitat for life. ○​ High Heat of Vaporization: It takes a lot of energy to turn water into vapor (e.g., sweating cools the body). ○​ Universal Solvent: Water dissolves many substances due to its polarity. 4. Acids, Bases, and pH  ​ Acids: Release H⁺ ions in water, lowering pH (more acidic). ​ Bases: Release OH⁻ ions in water, raising pH (more basic). ​ pH Scale: Measures the concentration of H⁺ ions in a solution. ○​ pH 7: Neutral (pure water). ○​ pH < 7: Acidic. ○​ pH > 7: Basic. ​ Buffers: Help maintain stable pH levels in living organisms (e.g., blood pH is maintained between 7.35 and 7.45). 5. Chemical Reactions ​ Reactants → Products: Chemical reactions involve breaking and forming bonds. ​ Activation Energy: The energy needed to start a reaction. ​ Hydrolysis: Breaks down complex molecules into simpler ones by adding water. ​ Condensation: Combines simpler molecules into complex ones, releasing water.