Atoms and molecules
60 flashcards covering Atoms and molecules for the ACT Science section.
Atoms are the fundamental building blocks of all matter, consisting of tiny particles like protons, neutrons, and electrons that combine to form elements such as hydrogen or carbon. Molecules, on the other hand, are groups of two or more atoms bonded together, creating compounds like water (H2O) or carbon dioxide. Understanding these concepts is essential because they explain the structure and behavior of everyday substances, from air we breathe to the materials in our bodies.
On the ACT Science section, atoms and molecules appear in questions that test your ability to interpret data from experiments, analyze graphs showing atomic interactions, or evaluate scientific passages on chemical properties. Common traps include confusing atomic mass with molecular weight or overlooking how temperature affects molecular bonds, so pay close attention to details in diagrams and tables. Focus on mastering basic definitions, periodic table trends, and simple reactions to handle these questions effectively.
A helpful tip: Practice sketching simple atom and molecule diagrams to visualize their differences.
Terms (60)
- 01
Atom
An atom is the basic unit of matter, consisting of a nucleus with protons and neutrons surrounded by electrons, and it is the smallest unit of an element that retains the element's properties.
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Molecule
A molecule is a group of two or more atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.
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Element
An element is a substance made up of only one type of atom, and it cannot be broken down into simpler substances by chemical means.
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Compound
A compound is a substance formed when two or more different elements are chemically bonded in a fixed ratio, resulting in new properties different from its components.
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Proton
A proton is a positively charged subatomic particle found in the nucleus of an atom, with a mass of approximately 1 atomic mass unit, and its number defines the element's atomic number.
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Neutron
A neutron is a neutral subatomic particle found in the nucleus of an atom, with a mass similar to a proton, and it contributes to the atom's mass but not its charge.
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Electron
An electron is a negatively charged subatomic particle that orbits the nucleus of an atom, and its arrangement determines the atom's chemical behavior and bonding.
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Atomic number
The atomic number is the number of protons in the nucleus of an atom, which defines the element and its position in the periodic table.
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Mass number
The mass number is the total number of protons and neutrons in the nucleus of an atom, used to calculate the atom's approximate mass.
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Isotopes
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses.
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Atomic mass
Atomic mass is the weighted average mass of an element's isotopes, based on their abundance, and it is listed on the periodic table.
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Periodic table
The periodic table is a chart organizing all known elements by increasing atomic number, with elements in the same column sharing similar chemical properties.
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Groups in periodic table
Groups are the vertical columns in the periodic table, where elements have the same number of valence electrons and exhibit similar chemical behaviors.
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Periods in periodic table
Periods are the horizontal rows in the periodic table, indicating the number of electron shells in the atoms of the elements within that row.
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Metals
Metals are elements on the left side of the periodic table that typically conduct heat and electricity well, are malleable, and lose electrons to form positive ions.
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Nonmetals
Nonmetals are elements on the right side of the periodic table that generally do not conduct electricity well and tend to gain electrons to form negative ions.
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Metalloids
Metalloids are elements along the staircase line on the periodic table that have properties of both metals and nonmetals, such as silicon, which is a semiconductor.
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Valence electrons
Valence electrons are the electrons in the outermost shell of an atom, which determine how the atom bonds with others and its chemical reactivity.
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Ionic bond
An ionic bond is a type of chemical bond formed when one atom transfers electrons to another, resulting in the attraction between oppositely charged ions.
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Covalent bond
A covalent bond is a type of chemical bond where atoms share one or more pairs of electrons to achieve a stable electron configuration.
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Chemical formula
A chemical formula is a symbolic representation of a compound's composition, showing the types and ratios of atoms present, such as H2O for water.
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Molecular formula
A molecular formula shows the actual number of atoms of each element in a molecule, like C6H12O6 for glucose.
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Empirical formula
An empirical formula is the simplest whole-number ratio of atoms in a compound, such as CH2O for glucose, which is derived from its molecular formula.
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Mole
A mole is a unit representing 6.022 × 10^23 particles of a substance, used to measure amounts of atoms or molecules in chemical calculations.
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Avogadro's number
Avogadro's number is 6.022 × 10^23, the number of particles in one mole of a substance, allowing conversion between moles and actual particles.
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Diatomic molecules
Diatomic molecules are molecules consisting of two atoms, such as O2 or N2, which are the most common form of some elements at room temperature.
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Noble gases
Noble gases are elements in Group 18 of the periodic table, like helium and neon, which have full valence shells and are chemically inert.
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Alkali metals
Alkali metals are elements in Group 1 of the periodic table, such as sodium, which are highly reactive and readily lose one valence electron to form ions.
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Halogens
Halogens are elements in Group 17 of the periodic table, like chlorine, which are highly reactive nonmetals that need one electron to complete their valence shell.
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Electron configuration
Electron configuration is the arrangement of electrons in an atom's energy levels and orbitals, following the Aufbau principle, such as 1s2 2s2 for carbon.
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Ion
An ion is an atom or molecule that has gained or lost one or more electrons, resulting in a net electrical charge, such as Na+ or Cl-.
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Cation
A cation is a positively charged ion formed when an atom loses one or more electrons, typically metals like sodium becoming Na+.
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Anion
An anion is a negatively charged ion formed when an atom gains one or more electrons, typically nonmetals like chlorine becoming Cl-.
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Oxidation number
The oxidation number is a value assigned to an atom in a compound that indicates its degree of oxidation, based on assumed electron gain or loss.
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Chemical reaction
A chemical reaction is a process where reactants are converted into products through the breaking and forming of chemical bonds, often involving energy changes.
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Reactants
Reactants are the starting substances in a chemical reaction that undergo change to form products, as seen in the equation 2H2 + O2 → 2H2O.
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Products
Products are the substances formed as a result of a chemical reaction, such as water in the reaction 2H2 + O2 → 2H2O.
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Balancing chemical equations
Balancing chemical equations involves adjusting coefficients to ensure the number of atoms of each element is the same on both sides, following the law of conservation of mass.
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Law of conservation of mass
The law of conservation of mass states that matter is neither created nor destroyed in a chemical reaction, so the total mass of reactants equals the total mass of products.
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Solid state of matter
In the solid state, particles are closely packed in a fixed arrangement, giving the substance a definite shape and volume.
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Liquid state of matter
In the liquid state, particles are close together but can move past each other, resulting in a definite volume but no fixed shape.
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Gas state of matter
In the gas state, particles are far apart and move freely, causing the substance to have no definite shape or volume.
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Phase changes
Phase changes are transitions between states of matter, such as melting from solid to liquid, driven by changes in temperature or pressure.
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Kinetic molecular theory
The kinetic molecular theory explains the behavior of gases, stating that gas particles are in constant random motion and collisions determine pressure.
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Diffusion
Diffusion is the process by which particles spread from an area of higher concentration to lower concentration, such as a drop of ink dispersing in water.
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Ideal gas law
The ideal gas law, PV = nRT, relates pressure, volume, number of moles, and temperature of a gas, assuming ideal behavior under various conditions.
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Boyle's law
Boyle's law states that for a given amount of gas at constant temperature, pressure and volume are inversely proportional, so P1V1 = P2V2.
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Charles's law
Charles's law states that for a given amount of gas at constant pressure, volume is directly proportional to temperature, so V1/T1 = V2/T2.
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Gay-Lussac's law
Gay-Lussac's law states that for a given amount of gas at constant volume, pressure is directly proportional to temperature, so P1/T1 = P2/T2.
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Dalton's law of partial pressures
Dalton's law states that the total pressure of a mixture of gases is the sum of the partial pressures of each individual gas.
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Avogadro's law
Avogadro's law states that equal volumes of different gases at the same temperature and pressure contain an equal number of molecules.
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Stoichiometry
Stoichiometry is the calculation of reactants and products in chemical reactions based on the balanced equation, using mole ratios.
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Limiting reactant
The limiting reactant is the substance that is completely consumed first in a chemical reaction, determining the amount of product formed.
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Percent yield
Percent yield is the ratio of the actual amount of product obtained from a reaction to the theoretical amount, multiplied by 100 to show efficiency.
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Molarity
Molarity is a measure of concentration defined as the number of moles of solute per liter of solution, used in dilution and reaction calculations.
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Solubility
Solubility is the maximum amount of a substance that can dissolve in a given amount of solvent at a specific temperature, often expressed in grams per 100 mL.
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Acid
An acid is a substance that donates hydrogen ions in water, resulting in a pH less than 7 and turning litmus paper red.
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Base
A base is a substance that accepts hydrogen ions or donates hydroxide ions in water, resulting in a pH greater than 7 and turning litmus paper blue.
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pH scale
The pH scale measures the acidity or basicity of a solution from 0 to 14, where 7 is neutral, below 7 is acidic, and above 7 is basic.
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Electrolyte
An electrolyte is a substance that, when dissolved in water, produces ions that conduct electricity, such as sodium chloride in solution.