UPCAT Chemistry — Periodic Table, Bonding & Chemical LanguageStudy Notes

The periodic table is like a giant map of all known elements, arranged by their atomic number (number of protons). Think of it as a filing system where elements with similar properties are grouped together. A period is a horizontal row, while a group is a vertical column. Elements in the same group have similar chemical behaviors because they have the same number of valence electrons. For example, all Group 1 elements (alkali metals) like sodium and potassium react violently with water, while all Group 18 elements (noble gases) like helium and neon are very unreactive.

The periodic table shows predictable patterns in how element properties change. As you move across a period from left to right, atoms get smaller because the nuclear charge increases, pulling electrons closer. As you move down a group, atoms get larger because you're adding electron shells. These size changes affect other properties like ionization energy (energy needed to remove an electron) and electronegativity (tendency to attract electrons). Understanding these trends helps predict how elements will behave in chemical reactions.

Atoms rarely exist alone in nature - they form bonds to become more stable. There are three main types of chemical bonds. Ionic bonds form when electrons are completely transferred from metals to nonmetals, creating charged ions that attract each other (like NaCl - table salt). Covalent bonds form when nonmetals share electrons (like H2O - water). Metallic bonds occur in metals where electrons form a 'sea' that holds metal atoms together. The type of bond depends on the electronegativity difference between atoms.

While chemical bonds hold atoms together within molecules, intermolecular forces of attraction (IMFAs) are weaker forces that act between different molecules. London dispersion forces are the weakest and occur between all molecules due to temporary electron movement. Dipole-dipole forces occur between polar molecules. Hydrogen bonding is a special, stronger type of dipole force that occurs when hydrogen is bonded to fluorine, oxygen, or nitrogen. Ion-dipole forces are the strongest and occur between ions and polar molecules, like when salt dissolves in water.

Chemists use different types of formulas to represent compounds. The molecular formula shows the actual number of each type of atom (like C6H12O6 for glucose). The empirical formula shows the simplest whole-number ratio of atoms (like CH2O for glucose). Structural formulas (Lewis structures) show how atoms are connected. To draw Lewis structures, count valence electrons, determine bonding patterns, and place lone pairs. Some molecules have resonance structures - multiple valid ways to arrange electrons that must be considered together.

The Valence Shell Electron Pair Repulsion (VSEPR) theory helps predict molecular shapes. Electron pairs around atoms repel each other and arrange themselves to minimize repulsion. The molecular shape depends on the number of bonding and lone electron pairs. Common shapes include linear (2 bonds), trigonal planar (3 bonds), tetrahedral (4 bonds), and bent (when lone pairs are present). Molecular shape affects properties like polarity - symmetrical molecules are usually nonpolar, while asymmetrical ones are polar.

Chemical nomenclature is the systematic way of naming compounds. For ionic compounds, name the metal first (cation), then the nonmetal with an '-ide' ending (anion). When metals can form multiple charges, use Roman numerals. For covalent compounds between nonmetals, use Greek prefixes (mono-, di-, tri-, etc.) to indicate the number of atoms. Acids have special names: binary acids use 'hydro-' prefix and '-ic' ending, while oxyacids use '-ic' and '-ous' endings depending on oxygen content.

Intermolecular forces significantly affect the physical properties of substances. Substances with stronger IMFAs have higher boiling points because more energy is needed to separate molecules. They also have lower vapor pressure (less tendency to evaporate), higher surface tension (stronger attraction at the surface), and higher viscosity (more resistance to flow). These concepts explain why water has a high boiling point compared to similar-sized molecules, why honey flows slowly, and why some liquids form droplets while others spread out.