Chemistry explained questions and answers: 1st Semester (Chapters 1-3)

What is the fundamental difference between physical and chemical changes? ️ A physical change alters form or state without changing composition, while a chemical change produces new substances with different compositions How does the law of conservation of mass apply in chemical reactions? ️ The total mass of reactants equals the total mass of products because matter is neither created nor destroyed What defines an element in chemistry? ️ A pure substance made of only one type of atom that cannot be broken down chemically What is an atom composed of? ️ Protons, neutrons, and electrons How do isotopes differ from each other? ️ They have the same number of protons but different numbers of neutrons What is the significance of atomic number? ️ It determines the number of protons and defines the identity of an element How does atomic mass differ from mass number? ️ Atomic mass is the weighted average of isotopes, while mass number is the total of protons and neutrons in one atom What is a molecule? ️ A group of two or more atoms chemically bonded together How are compounds different from mixtures? ️ Compounds have fixed ratios and chemical bonds, while mixtures are physical combinations with variable composition What is the role of electrons in chemical bonding? ️ Electrons are shared or transferred to form bonds between atoms What is an ion? ️ An atom or molecule that has gained or lost electrons and carries a charge How are cations and anions different? ️ Cations are positively charged, while anions are negatively charged 2 What is electronegativity? ️ The ability of an atom to attract electrons in a bond How does electronegativity affect bond type? ️ Large differences create ionic bonds, small differences create covalent bonds What is a covalent bond? ️ A bond formed by sharing electrons between atoms What is an ionic bond? ️ A bond formed by transfer of electrons from one atom to another What is the octet rule? ️ Atoms tend to gain, lose, or share electrons to achieve eight valence electrons What is a valence electron? ️ An electron in the outermost energy level of an atom How does the periodic table organize elements? ️ By increasing atomic number and recurring chemical properties What is a group in the periodic table? ️ A vertical column of elements with similar properties What is a period in the periodic table? ️ A horizontal row of elements Why do elements in the same group behave similarly? ️ They have the same number of valence electrons What is metallic character? ️ The tendency of an element to lose electrons and form positive ions What is ionization energy? ️ The energy required to remove an electron from an atom How does atomic radius change across a period? ️ It decreases from left to right How does atomic radius change down a group? ️ It increases due to added electron shells What is a chemical formula? ️ A representation of the types and numbers of atoms in a compound 3 What does a coefficient in a chemical equation represent? ️ The number of molecules or moles involved What is a balanced chemical equation? ️ An equation with equal numbers of each type of atom on both sides What is a reactant? ️ A starting substance in a chemical reaction What is a product? ️ A substance formed in a chemical reaction What is the mole concept? ️ A unit representing 6.022 × 1023 particles What is molar mass? ️ The mass of one mole of a substance How do you convert grams to moles? ️ Divide mass by molar mass What is Avogadro’s number? ️ The number of particles in one mole What is a limiting reagent? ️ The reactant that is completely consumed first in a reaction What is percent yield? ️ The ratio of actual yield to theoretical yield expressed as a percentage What is theoretical yield? ️ The maximum amount of product predicted by stoichiometry What is empirical formula? ️ The simplest whole-number ratio of atoms in a compound What is molecular formula? ️ The actual number of atoms of each element in a molecule What is a solution? ️ A homogeneous mixture of solute and solvent What is a solute? ️ The substance being dissolved