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General Chemistry Unit Exam #1 Concept Guide

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이 집합의 용어 (28)

  • What is the difference between pure substances and mixtures?

    Pure substances have a fixed composition and distinct properties, while mixtures contain two or more substances physically combined with variable composition.

  • Define elements and compounds.

    Elements are pure substances made of only one type of atom. Compounds are pure substances composed of two or more elements chemically combined in fixed ratios.

  • What distinguishes homogeneous from heterogeneous mixtures?

    Homogeneous mixtures have uniform composition throughout, while heterogeneous mixtures have visibly different parts or phases.

  • What is the law of constant composition (law of definite proportions)?

    It states that a given compound always contains the same elements in the same proportion by mass.

  • Differentiate physical and chemical properties.

    Physical properties can be observed without changing the substance's identity; chemical properties describe a substance's ability to undergo chemical changes.

  • What is the difference between physical and chemical change?

    Physical change alters appearance but not composition; chemical change results in new substances with different compositions.

  • Explain intensive vs extensive properties.

    Intensive properties do not depend on amount (e.g., density); extensive properties depend on amount (e.g., mass, volume).

  • What are basic and derived units in measurement?

    Basic units are fundamental SI units (e.g., meter, kilogram); derived units are combinations of basic units (e.g., volume = cubic meters).

  • What is the difference between exact and inexact numbers?

    Exact numbers have no uncertainty (e.g., counted items); inexact numbers are measured and have uncertainty.

  • List the SI base units for length, mass, time, temperature, volume, and amount of substance.

    Length: meter (m), Mass: kilogram (kg), Time: second (s), Temperature: kelvin (K), Volume: cubic meter (m3), Amount: mole (mol).

  • What is the difference between precision and accuracy in measurements?

    Precision refers to reproducibility of measurements; accuracy refers to closeness to the true value.

  • What are significant figures and why are they important?

    Significant figures indicate the precision of a measurement and are used to reflect uncertainty in calculations.

  • What is dimensional analysis used for?

    It is a method to convert units and solve problems by using conversion factors to ensure consistent units.

  • Name the three main subatomic particles and their charges.

    Protons (+1), Neutrons (0), Electrons (-1).

  • What is the atomic number of an element?

    The atomic number is the number of protons in the nucleus of an atom.

  • How is mass number defined?

    Mass number is the total number of protons and neutrons in an atom's nucleus.

  • Define ion, cation, and anion.

    An ion is an atom or molecule with a net charge. Cations are positively charged ions; anions are negatively charged ions.

  • What is an isotope?

    Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

  • How do you write an isotope (nuclide) symbol?

    Use \(^A_ZX\) where X is the element symbol, Z is atomic number, and A is mass number.

  • How is average atomic mass calculated?

    It is the weighted average of the masses of an element's isotopes based on their relative abundances.

  • What is the difference between empirical and molecular formulas?

    Empirical formula shows the simplest whole-number ratio of atoms; molecular formula shows the actual number of atoms in a molecule.

  • What are the rows and columns of the periodic table called?

    Rows are called periods; columns are called groups.

  • How does atomic number change across a period?

    Atomic number increases by one moving left to right across a period.

  • How are elements in the same group related?

    Elements in the same group have similar chemical properties and the same number of valence electrons.

  • Name the main element groups on the periodic table.

    Halogens, noble gases, alkali metals, alkaline earth metals, transition metals, main-group elements, lanthanides, and actinides.

  • Where are metals, metalloids, and nonmetals located on the periodic table?

    Metals are on the left and center, metalloids along the zigzag line, and nonmetals on the right side.

  • Which elements are diatomic (the 'big seven')?

    H2, N2, O2, F2, Cl2, Br2, I2.

  • What is the distinction between molecular and ionic compounds?

    Molecular compounds consist of molecules formed by covalent bonds; ionic compounds consist of ions held by ionic bonds.