U3 Biochemistry: Atoms, Compounds, & Elements. Chemical bonds. – Flashcards
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neutrons
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the neutral particles located in the nucleus of the atom
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elements
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a substance that cannot be broken down into other substances
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isotopes
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atoms of the same element that have different numbers of neutrons
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compound
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a pure substance formed when two or more different elements combine in a fixed ratio
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molecule
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a compound in which the atoms are held together by covalent bonds
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covalent bonds
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a chemical bond that forms when atoms share electrons
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ionic bonds
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a chemical bond that forms when atoms lose or gain electrons
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iodine
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used in a hormone produced by thyroid gland
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fluorine
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used in fluoride to prevent tooth decay
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list three trace elements
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iodine, iron, flourine
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What make up 96% of human body weight
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hydrogen, oxygen, nitrogen, carbon
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atomic number
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number of protons in an atom
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mass number
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sum of the number of protons and neutrons in an atom's nucleus
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radioactive isotopes
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when a nucleus is unstable and decays spontaneously
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What is involved in the chemical activity of an atom?
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Only electrons
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True or false: the farther an electron is from the positively charged nucleus, the greater the energy.
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true
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each orbital can hold a max of __ electrons
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two
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What determines the chemical properties of an atom?
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the number of electrons in the valence shell
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define covalent bond
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two or more atoms share one or more pairs of valence electrons to form molecules
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what is electronegativity
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different attractions for shared electrons
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define nonpolar covalent
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when atoms have the same electronegativity
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what are molecules called when atoms have different electronegativity?
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polar covalent
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define ionic bonds
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the attraction between ions with opposite charges
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define ions
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when electronegativity is unequal, electrons can be stripped to charged particles called ions
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cations
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positive because they lose electrons
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anions
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negative because they gain electrons
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What is the weakest bond?
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hydrogen bond
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where do hydrogen bonds occur?
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in polar covalent molecules resulting in a partial positive for hydrogen
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what are positively charged hydrogen attracted to?
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partially negative atom of another molecule
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What are reactants converted into during chemical reactions?
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products
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What is conserved in a chemical reaction?
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matter
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define electron shells
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the energy levels that electrons move around the nucleus in
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