PRE-IB Chemistry Notes (based on your test) 1. Molecular Formula English A molecular formula shows the actual number of atoms in a molecule. Example: * H₂O = 2 hydrogen atoms and 1 oxygen atom * C₆H₁₂O₆ = 6 carbon, 12 hydrogen, 6 oxygen Important * Molecular formula = actual number * Empirical formula = simplest ratio Example: * Molecular formula: C₆H₁₂O₆ * Empirical formula: CH₂O Test question “What information does the molecular formula provide?” Correct answer: ✅ The actual numbers of atoms in a molecule ⸻ Русский Молекулярная формула показывает настоящее количество атомов в молекуле. Пример: * H₂O = 2 атома водорода и 1 атом кислорода * C₆H₁₂O₆ = 6 углеродов, 12 водородов, 6 кислородов Важно * Molecular formula = настоящее количество * Empirical formula = простое соотношение ⸻ 2. Isotopes English Isotopes are atoms of the same element with: * same number of protons * different number of neutrons Example: * Carbon-12 * Carbon-14 Both have: * 6 protons But different neutrons. Formula Neutrons = mass number − atomic number ⸻ Русский Изотопы — это атомы одного элемента: * одинаковое количество протонов * разное количество нейтронов Формула: Нейтроны = массовое число − атомный номер ⸻ 3. Protons, Neutrons and Electrons English Proton number = atomic number Electron number Neutral atom: electrons = protons Ion: * positive ion → lost electrons * negative ion → gained electrons Example ^{43}_{20}Ca^{2+} * protons = 20 * neutrons = 43 − 20 = 23 * electrons = 20 − 2 = 18 ⸻ Русский Протоны = атомный номер Электроны У нейтрального атома: электроны = протоны Ион: * плюс → потерял электроны * минус → получил электроны Пример: Ca²⁺: * 20 протонов * 23 нейтрона * 18 электронов ⸻ 4. Electron Configuration English Electrons fill shells. Rules * 1st shell = 2 electrons * 2nd shell = 8 * 3rd shell = 8 Examples Mg (12): 2,8,2 Cl (17): 2,8,7 Al (13): 2,8,3 Outer shell electrons Mg → 2 Cl → 7 ⸻ Русский Электроны распределяются по оболочкам. Примеры: * Mg = 2,8,2 * Cl = 2,8,7 * Al = 2,8,3 Внешние электроны: * Mg → 2 * Cl → 7 ⸻ 5. Ionic Bonding English Ionic bonding happens when electrons are transferred. * metals lose electrons * non-metals gain electrons Example: Mg + Cl Mg loses 2 electrons. Each chlorine gains 1. Formula: MgCl₂ ⸻ Русский Ионная связь появляется, когда электроны переходят от одного атома к другому. * металл теряет электроны * неметалл получает Пример: MgCl₂ ⸻ 6. Relative Atomic Mass and Relative Formula Mass English Relative Atomic Mass (Ar) Average mass of atoms compared with carbon-12. Example: Cl = 35.5 Relative Formula Mass (Mr) Total of all atomic masses in a formula. Example: H₂O = 2(1) + 16 = 18 ⸻ Русский Relative Atomic Mass Средняя масса атомов элемента. Relative Formula Mass Сумма всех атомных масс в формуле. Пример: H₂O = 18 ⸻ 7. Moles English Formula triangle n=\frac{m}{M} n = moles m = mass M = molar mass Example NaCl: M = 23 + 35.5 = 58.5 If mass = 117 g 117 ÷ 58.5 = 2 mol ⸻ Русский Формула: n = m / M n — моли m — масса M — молярная масса ⸻ 8. Concentration English Formula: c=\frac{n}{V} c = concentration n = moles V = volume in dm³ Important 1000 cm³ = 1 dm³ ⸻ Русский Формула: c = n / V V обязательно в dm³ 1000 cm³ = 1 dm³ ⸻ 9. Acids and Alkalis English Acid Produces H⁺ ions Alkali Produces OH⁻ ions Examples: * HCl = acid * NaOH = alkali ⸻ Русский Кислота выделяет H⁺ Щёлочь выделяет OH⁻ ⸻ 10. Strong and Weak Acids English Strong acid Fully ionizes in water. Example: HCl Weak acid Partially ionizes. Example: CH₃COOH Important Strong ≠ concentrated ⸻ Русский Сильная кислота полностью распадается. Слабая — только частично. ⸻ 11. Amphoteric Compounds English Amphoteric substances can act as: * acid * base Example: Al₂O₃ ⸻ Русский Амфотерные вещества могут быть: * кислотой * основанием ⸻ 12. pH and Indicators English pH scale * below 7 = acid * 7 = neutral * above 7 = alkali Indicators Litmus: * acid → red * alkali → blue Phenolphthalein: * acid → colorless * alkali → pink ⸻ Русский pH: * меньше 7 = кислота * 7 = нейтрально * больше 7 = щёлочь ⸻ 13. Acid-Base Titration English Titration is used to find concentration. Steps 1. Add indicator 2. Add acid/base slowly 3. Endpoint color change 4. Use formula Common indicators * phenolphthalein * methyl orange ⸻ Русский Титрование используют для нахождения концентрации. Шаги: 1. Добавить индикатор 2. Медленно добавлять раствор 3. Смотреть изменение цвета ⸻ 14. Redox Reactions English Oxidation Loss of electrons Reduction Gain of electrons OIL RIG: * Oxidation Is Loss * Reduction Is Gain ⸻ Русский Окисление = потеря электронов Восстановление = получение электронов ⸻ 15. Hydrophobic and Hydrophilic English Hydrophobic “Water-fearing” Does not mix with water. Example: oil Hydrophilic “Water-loving” Mixes with water. Example: salt ⸻ Русский Hydrophobic: не смешивается с водой Hydrophilic: смешивается с водой ⸻ 16. Organic Chemistry Naming (IMPORTANT FOR TEST) English Alkane Only single bonds General formula: C_nH_{2n+2} Alkene Contains double bond General formula: C_nH_{2n} Alkyne Contains triple bond General formula: C_nH_{2n-2} ⸻ Русский Алкан: только одинарные связи Алкен: двойная связь Алкин: тройная связь ⸻ 17. IUPAC Naming Quick Rules English Step 1 Find longest chain. Step 2 Count carbons: * meth = 1 * eth = 2 * prop = 3 * but = 4 * pent = 5 * hex = 6 Step 3 Find double bond. Step 4 Number chain from nearest double bond. Step 5 Name branches: * methyl * ethyl ⸻ Русский 1. Найти самую длинную цепь 2. Посчитать углероды 3. Найти двойную связь 4. Нумеровать с ближайшей двойной связи 5. Назвать ответвления ⸻ 18. Combustion English Combustion = burning in oxygen. Example: C_5H_{12}+8O_2\rightarrow5CO_2+6H_2O Products: * carbon dioxide * water ⸻ Русский Горение — реакция с кислородом. Продукты: * CO₂ * H₂O ⸻ 19. Activity Series English More reactive metals replace less reactive metals. Mg is more reactive than H: → reacts with acid Cu is less reactive than Fe: → cannot replace Fe ⸻ Русский Более активный металл вытесняет менее активный

Molecular Formula

Shows the actual number of atoms in a molecule.

Empirical Formula

Represents the simplest ratio of elements in a compound.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons.

Neutrons Formula

Neutrons = mass number − atomic number.

Proton Number

Also known as atomic number, represents the number of protons in an atom.

Electron Configuration

Arrangement of electrons in shells around the nucleus.

Ionic Bonding

Occurs when electrons are transferred from metals to non-metals.

Relative Atomic Mass (Ar)

Average mass of atoms compared with carbon-12.

Relative Formula Mass (Mr)

Total of all atomic masses in a chemical formula.

Moles Formula

n = m / M, where n is moles, m is mass, and M is molar mass.

Concentration Formula

c = n / V, where c is concentration, n is moles, and V is volume in dm³.

Acid

Produces H⁺ ions in solution.

Alkali

Produces OH⁻ ions in solution.

Strong Acid

Fully ionizes in water.

Weak Acid

Partially ionizes in solution.

Amphoteric Compounds

Substances that can act as both acids and bases.

pH Scale

Measures the acidity or alkalinity of a solution; below 7 is acidic, 7 is neutral, above 7 is alkaline.

Titration

Technique used to determine the concentration of a solution.

Oxidation

Loss of electrons in a chemical reaction.

Reduction

Gain of electrons in a chemical reaction.

Hydrophobic

Substances that do not mix with water.

Hydrophilic

Substances that mix with water.

Alkane

Hydrocarbons with only single bonds; general formula C_nH_{2n+2}.

Alkene

Hydrocarbons with at least one double bond; general formula C_nH_{2n}.

Alkyne

Hydrocarbons with at least one triple bond; general formula C_nH_{2n-2}.

Combustion

Burning of a substance in oxygen to produce energy.

Activity Series

A list that ranks metals based on their reactivity.