A specific type of matter with a definite composition.
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Element
A pure substance that cannot be broken down into simpler substances by chemical means.
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Compound
A pure substance formed by the chemical combination of two or more different elements in fixed proportions. This can be broken down or decomposed into elements.
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Atom
The smallest unit of matter that retains the properties of an element.
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John Dalton
proposed the concept that matter is composed of atoms, regardless of its form.
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Subatomic particle
A particle smaller than an atom that constitutes the atom.
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Nucleus
The dense central core of an atom containing protons and neutrons.
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Proton
A positively charged subatomic particle found in the nucleus.
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Neutron
A neutral subatomic particle found in the nucleus.
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Electron
A negatively charged subatomic particle that orbits the nucleus.
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Nucleus
the core of an atom
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Electron Shells
A region of space surrounding the nucleus where electrons are likely to be found.
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Electron Clouds
the area around an atom's nucleus where electrons are most likely to be found.
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Atomic number
The number of protons in the nucleus of an atom.
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Mass number
The sum of the number of protons and neutrons in the nucleus of an atom.
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Atomic mass
Another term for mass number.
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Electron cloud model
Emphasizes the probabilistic nature of electron location.
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Probability distribution
The mathematical function that describes the likelihood of finding an electron at a particular point in space.
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Bohr model
Provides a simplified, visual representation of electron arrangement in energy levels.
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Outermost energy level
The highest energy level of an atom that contains electrons.
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Stable electron configuration
An atom with a filled outermost energy level (usually eight electrons).
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Energy level
A specific region of an atom where electrons have a particular amount of energy.
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Niels Bohr
A Danish physicist who proposed a model of the atom where electrons orbit the nucleus in specific energy levels. He won the Nobel Prize in Physics in 1922 for his contributions to the understanding of atomic structure.
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Chemical bond
A process that involves the rearrangement of atoms to form new substances with different properties.
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Octet rule
The tendency of atoms to gain, lose, or share electrons to achieve a stable electron configuration of eight electrons in the outermost energy level.
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Inert element
An element that is chemically unreactive due to a stable electron configuration.
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Isotope
Atoms of the same element with the same number of protons but different numbers of neutrons.
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Atomic weight
The average mass number of an element based on the abundance of its isotopes in nature.
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Carbon-13
an isotope of carbon that has seven neutrons instead of six.
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Carbon-14
an isotope of carbon that has eight neutrons instead of six.
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Radioactive isotope (radioisotope)
An unstable isotope that undergoes nuclear decay, emitting particles and radiation.
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Decay
The process by which a radioactive isotope breaks down, releasing particles and radiation.
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Radioactivity
The emission of radiation from an atom’s nucleus. It differs from chemical activity because it can change the number of protons in an atom.
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Alpha Particles
Are heavy particles consisting of two protons plus two neutrons.
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Beta Particles
Are electrons formed in a radioactive atom’s nucleus by one of its neutrons breaking down into a proton and an electron.
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Gamma Rays
Are electromagnetic radiation, a form of light energy.
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Chemical Bonds
A process formed from reactions that hold atoms together.
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Crystal
A solid material composed of atoms arranged in a regular, repeating pattern.
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Carbon dioxide
a molecule composed of one carbon atom and two oxygen atoms.
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Water
a molecule composed of two hydrogen atoms and one oxygen atom.
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Ionic Bond
A chemical bond formed by the transfer of electrons between atoms. Also called electrovalent bond.
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Ion
An atom that has gained or lost electrons, resulting in a net electrical charge. Can also be called, electrolytes.
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Cation
A positively charged ion, formed by losing electrons.
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Anion
A negatively charged ion, formed by gaining electrons.
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Electron Transfer
The process by which one atom donates an electron to another atom.
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Electrostatic Force
The attractive force between oppositely charged ions.
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Covalent Bond
A chemical bond formed by the sharing of electrons between atoms.
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Single Covalent Bond
A covalent bond where one pair of electrons is shared.
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Double Bond
A covalent bond where two pairs of electrons are shared.
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Hydrogen Bond
A weak attraction between a hydrogen atom bonded to a highly electronegative atom (oxygen, nitrogen, or fluorine) and another electronegative atom in a different molecule or part of the same molecule.
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Polar Molecule
A molecule with regions of positive and negative partial charges due to unequal electron distribution.
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Water
A polar molecule capable of forming hydrogen bonds with other water molecules.
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Nonpolar Molecule
A molecule with electrons shared equally among atoms, resulting in no polarity.
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Oil
A nonpolar molecule that does not form hydrogen bonds with water.
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Chemical Reaction
A process involving the rearrangement of atoms to form new substances.
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Reactants
The starting substances in a chemical reaction.
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Products
The substances formed as a result of a chemical reaction.
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Synthesis Reaction
A reaction where two or more reactants combine to form a more complex product. This requires energy input.
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Decomposition Reaction
A reaction where a complex substance breaks down into simpler substances. This reaction releases energy.
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Exchange Reaction
A reaction where two reactants exchange components to form two new products.
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Reversible Reaction
A reaction that can proceed in both directions.
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Metabolism
The sum of all chemical reactions occurring in the body.
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Catabolism
Chemical reactions that break down complex molecules into simpler ones, releasing energy.
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Hydrolysis
A catabolic reaction that uses water to break down molecules.
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Adenosine triphosphate
a molecule that stores and transfers energy.
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Anabolism
Chemical reactions that build complex molecules from simpler subunits.
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Dehydration Synthesis
An anabolic reaction that removes water to join molecules together.
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Biomolecules
Large organic molecules essential for life.
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Organic Compound
A compound containing carbon-carbon (C-C) or carbon-hydrogen (C-H) covalent bonds.
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Inorganic Compound
A compound typically not containing carbon or, if it does, lacking C-C or C-H bonds.
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Solvent
A substance capable of dissolving other substances.
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Solute
A substance dissolved in a solvent.
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Polarity
The property of having a positive and negative end.
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Hydration Shell
A layer of water molecules surrounding a charged solute.
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Specific Heat
The amount of heat required to raise the temperature of a substance by one degree.
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Oxygen (O₂)
A diatomic molecule essential for cellular respiration. It is required for the complete breakdown of nutrients and energy release.
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Carbon Dioxide (CO₂)
A simple inorganic compound involved in cellular respiration and acid-base balance. Produced as a waste product of nutrient breakdown and plays a role in acid-base balance.
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Electrolyte
A substance that dissociates into ions in solution. Large group of inorganic compounds that includes acids, bases, and salts.
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Dissociation
The process of breaking down into ions.
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Acids
Substances that release hydrogen ions (H⁺) in solution; also called proton donors.
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Bases
Substances that release hydroxide ions (OH⁻) or accept hydrogen ions (H⁺) in solution; also called proton acceptors.
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Strong acids
these dissociate completely, releasing many H⁺ ions.
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Weak acids
these dissociate minimally, releasing few H⁺ ions.
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Strong bases
these dissociate completely, releasing many OH⁻ ions.
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Weak bases
these dissociate minimally, releasing few OH⁻ ions.
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pH
A measure of the hydrogen ion concentration in a solution.
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neutrality
A pH of 7 indicates ___________ (equal amounts of H + and OH − )
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acidity
A pH of less than 7 indicates ___________ (more H + than OH − )
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alkalinity
A pH greater than 7 indicates ________________(more OH − than H + )
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pH Homeostasis
The maintenance of a stable pH in body fluids.
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Carbonic Acid
This acid contributes to the slightly lower pH of venous blood.
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Buffer
A substance that resists changes in pH by accepting or donating hydrogen ions. They act as a reservoir for hydrogen ions, accepting or donating them as needed.
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Salt
A compound formed by the reaction of an acid and a base.
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Neutralization Reaction
A reaction between an acid and a base that produces a salt and water.
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Hypercapnia
A condition where carbon dioxide concentration in the blood is abnormally high.
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Acidosis
A condition where the body's pH is lower than normal.
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oxins
Substances that can damage body molecules.
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Carbon Monoxide (CO)
A toxin that binds to hemoglobin, preventing oxygen transport.
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Mercury (Hg)
A toxin that damages cells by binding to sulfur-containing molecules.
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