Elements, Atoms & Electrons

• Here are your study notes

Elements

• Pure substances are composed of only one type of atom or molecule
• Atoms are comprised of protons, electrons, and neutrons.
• Protons have a positive charge.
• Electrons have a negative charge.
• Neutrons have no charge.
• Protons and neutrons reside in the nucleus, while electrons orbit in surrounding orbitals
• Atomic Number: equals the number of protons or electrons in an atom.
• Atomic Mass: equals the number of protons plus neutrons in an atom; the average mass is given
• Isotopes: The number of neutrons changes, altering the atomic mass, while the number of protons and electrons remains constant
• Unstable isotopes are radioactive and emit particles or energy.

Electrons

• Negatively charged, surround atomic nuclei
• They balance out positively charged protons for stability
• So small that mass isn't counted
• Electrons exist in an electron cloud, comprised of energy levels & orbitals
• Energy Levels: represented as K, L, M, ...
• Orbitals: S, P, D, F
• K-level: the lowest energy level, contains 2e- of a circular S orbital; can contain a maximum of 2e-
• L-level: includes S & P orbitals
• P orbitals are made of ‘dumbbell' shapes on x,y,z axes
• Each P orbital can hold 2e-, creating a total of 6e-
• S & P orbitals together hold a maximum of 8e-
• Valence Electrons-Outermost e- of atom
• Valence Electrons-Used in chemical reactions
• Valence Electrons-Determine the atom's reactivity

Reactivity and Bonding

• To achieve stability, atoms aim to fill their valence shell by giving, taking, or sharing in order to reach stability
• Nonstable atoms have nonneutral charges and become ions
• Atoms that give up an electron become cations (+).
• Atoms that take in an electrons become anions (-).
• 1 metal & 1 nonmetal give/take electrons
• Cation + Anion = neutral compound (ex- Na(+1) + Cl(-1) = NaCl)
• The ionic bond will be stronger the greater the difference in ion charges
• Ionic Bonding create polar bonds

Covalent Bonding

• Covalent Bonding entails two nonmetals that shares of electrons.
• Covalent Bonding makes three types of bonds
• Single; weakest
• Double; intermediate
• Triple; strongest
• Polarity depends

Properties of Water

• Electronegativity & Polarity
• Electronegative atom has high affinity for taking electrons; ex: Halogens (F, Cl, Br, I) and Oxygen
• Metals on the far left of the Periodic Table are the least electronegative and more readily gives up e-
• The greater the difference in electronegativity between atoms in a molecule, the more polar that molecule will be; ex. Water (H2O)
• Atoms with similar electronegativity will be less polar to nonpolar; ex. H2, F2
• Cohesion occurs because Water molecules stick to other water molecules due to hydrogen bonding
• Cohesion of water Creates a high surface tension; can be broken by a surfactant
• Adhesion is the process of water molecules sticking to to other polar, non-water molecules
• Water acts as the universal solvent as it Dissolves other polar compounds and hydrophilic compounds/ionic bonds
• Hydrophobic compounds are generally nonpolar and repel water

Water Reactions

• Dehydration Synthesis: Molecules combine and spit out a water molecule
• Hydrolysis: Molecules broken apart by presence of water

pH, Acids, Bases, Buffers

• pH Scale ranges From 0-14 where
  • 0-6 is acidic
  • 7 is neutral
  • 8-14 is basic/alkaline
• Acids: Release H+ ions (a proton) when dissolved in water
• Bases: OH- (hydroxide ions) absorb H+ ions, reducing acidity of solution
• Buffers: Resist changes in pH when small amounts of acids/bases are added; usually includes a salt

Functional Groups

• Hydroxyl Groups (R-OH): Single bonded to OH; found in alcohols; simplest = methanol/methylachohol
• Carbonyl Groups (R-C=O): Carbon double bonded to oxygen; found in multiple groups of compounds; ex- Aldehydes/formaldehyde; Esters make an "L" shape; Ketones make a "T" shape
• Carboxyl Groups: combination of hydroxyl and carbonyl groups; and the group that is Found in organic acids; formic acid
• Amino/Amine Groups: NH2; Found in amino acids/organic acids (carboxyl group) + amine group; Simplest = glycine

Macromolecules

• Carbohydrates are Made of carbon, oxygen, and hydrogen primarily
• Carbohydrates' C-H bonds contain energy for quick usage
• Carbohydrate Monomers = monosaccharides (can be aldehydes or ketones); simple sugars; ring shaped; end with suffix -ose
• Grouped by # of carbons; ex: Pentose (5), Hexose (6)
• Monosaccharides are combined into disaccharide polymers via dehydration synthesis
• Glucose can be made into disaccharides
• Hexose; has alpha & beta forms determined by the position of hydroxyl groups
• Glucose has a carbonyl group
• Fructose has a ketone
• Galactose is a mirror of glucose
• Alpha glucose + alpha glucose = Maltose
• Glucose + Fructose = Sucrose
• Glucose + Galactose = Lactose
• Polysaccharides
• Alpha glucose = branched polymer (Starches, glycogen)
• Beta glucose = unbranched polymer (Cellulose)
• Lipids
  • Comprised of C, O, H
  • C-H bonds contain energy for long-term storage
  • Lipids are hydrophobic/nonpolar
  • Examples of Lipids: oils, fats, waxes
  • Triglyceride: Glycerol + 3 fatty acids
  • Steroids
  • Cholesterol made from saturated fats
  • Hormones
• Glucose converted into starches, then excesses made into triglycerides by liver for energy storage
  • High Density Lipoprotein - HDL - "Good" cholesterol
  • Low Density Lipoprotein - LDL - "Bad" cholesterol
• Proteins consist of Monomers = amino acids that Contain amino & carboxyl groups, and amine/organic acids
• Protein's simplest form is glycine
• Peptide bonds link monomers into polymers
• Polypeptides named by the number of amino acids being bonded together
• Ex: 2 amino acids bound by 1 peptide bond = dipeptide

Polypeptide Structures

• Primary sequence: amino acid sequence
• Secondary sequence: primary sequences together in 3D space
  • Alpha helices
  • Beta pleated sheets
• Tertiary sequence: Secondary structures folded back on each other
  • Globular proteins
  • Enzymes
• Quaternary sequence: Multiple tertiary structures together
  • Hemoglobin, hemocyanin
• Enzymes cont'd
• Act as Tertiary proteins, catalyze reactions, and end in -ase
• Specific substrates bind to specific active sites
• Denatured by heat; bonds break and lose function

Nucleic Acids

• The three major components of nucleotide monomers:
  • Pentose sugar
  • Phosphate group
  • Nitrogenous base
• Nitrogenous Bases cont'd
  • Purines; 2 ring structure (Adenine, Guanine)
  • Pyrimidines; 1 ring structure (Thymine, Cytosine, Uracil)
• Purines & pyrimidines bond to one another across DNA strands with hydrogen bonds: A&T/U, G&C
• Deoxyribonucleic Acid (DNA) is a Double stranded helix
• Its Deoxyribose sugar Uses Thymine
• Ribonucleic Acid (RNA) is a Single strand, Ribose sugar
• Ribonucleic Acid Uses uracil

Study notes cover the basics of elements, atoms and electrons. Topics include the definition of pure substances, the components of an atom (protons, electrons, and neutrons), atomic number, atomic mass and isotopes.