Chemistry: Unit 5 Study Guide – Flashcards
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How do atoms in nature become stable?
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by forming chemical bonds
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A ___ is a mutual electrical attraction between the nuclei and valence electrons of different atoms which holds them together
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chemical bond
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Chemical bonds form as atoms ___
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transfer and share valence electrons
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By creating chemical bonds atoms ___ their individual potential energy and create a ___ form of matter.
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decrease; more stable
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What do atoms do when they form ionic bonds?
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they transfer valence electrons; generally between a metal and nonmetal
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What do atoms do when they form covalent bonds?
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they share valence electron and generally form between nonmetals
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Metallic bonding in characterized by metal atoms a "sea" of ___ valence electrons.
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delocalized
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What do chemical bonds do for bonded atoms?
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they produce stable electron configurations for them
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In most cases for the main group elements, a stable electron configuration resembles which group of elements?
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noble gases
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define stable octet
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a stable electron configuration which consists of 8 electrons in the highest occupied s and p orbitals
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the ___ states that for main group elements, chemical bonds tend to form so that each atom, by gaining, losing, or sharing valence electrons, achieves an octet of electrons in its highest occupied level
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octet rule
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T/F: there are no exceptions to the octet rule
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F
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what is a binary compound
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a compound which is composed of only 2 different elements
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Ionic compounds form so that the number of positive charges (+) and the number of negative charges (-) are ___.
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equal
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most ionic compounds exist as ___.
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crystalline solids
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What does a crystal represent?
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the lowest potential energy arrangement of ions
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Describe HOW ionic compounds generally form
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as large quantities of ions spontaneously arrange themselves in their lowest energy arrangement
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the ___ of an ionic compound is an orderly arrangement of ions which represents the lowest potential energy
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crystal lattice
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a ___ is the smallest portion of a crystal lattice that shows the 3 dimensional pattern of the entire lattice
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unit cell
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What are 2 ways that an ionic crystal can form?
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when ionic solids are melted ans allowed to cool; when an ionic compound is dissolved in water and the water is allowed to evaporate
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What are oxides?
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metals ionically bonded to to oxygen
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What does the geometry of an ionic crystal depend on>
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the sizes of the ions and the ration of ions which balance electrical charge
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The greater the ___ the ___ the ionic bond
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lattice energy; stronger
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What is a formula unit?
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the simplest collection of ions from which an ionic compound's formula can be established
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Al₂S₃
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formula unit for a compound that forms between Al and S
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What happens to the valence electrons of metal atoms during metallic bonding?
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they can delocalize
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___ are electrons which are free to move between empty orbitals of metal atoms
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delocalized valence electrons
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What gives metals their metallic properties
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delocalized electrons
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3 main metallic properties
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electrical conductivity, lusterm, malleability
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delocalized electrons can "flow" within a metal creating high electrical conductivity and heat transfer
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electrical conductivity
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delocalized electrons can absorb a wide variety of wavelengths of light and become excited, easily giving the appearance of "shine" when electrons drop back down to their ground state
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luster
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delocalized electrons can "shift position" if any stress is placed on a metallic bond
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malleability
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a ___ is a neutral group of atoms held together with covalent bonds. It is the simplest particle of a molecular compound
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molecule
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describe how molecules form
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atoms join together and are held by chemical bonds; they are either formed by the transfer of electrons (ionic), the sharing of electrons (covalent), or the sharing of a sea of delocalized electrons (metallic)
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What does a molecular formula represent?
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the chemical formula for a molecular compound, so they show the exact number of atoms of each element in a molecule
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Describe the formation of a covalent bond (hydrogen)
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individual hydrogen atoms approach each other; as atoms near each other, they experience attractive and repulsive forces between them; attractive forces outweigh repulsive forces and atoms move towards each other lowering their potential energy as they move together; continue to move together until there is a balance between the attractive and repulsive forces, balance achieved when the atoms are a set distance from each other
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chemical bonds represent the ___ for the bonded atoms
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lowest potential energy state
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what is required to break a covalent bond?
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same amount of energy that was released when the bond formed
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what is bond energy
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the amount of energy required to break a chemical bond and form neutral isolated atoms
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a covalent bond in which only one pair of electrons is shared between two atoms
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single bond
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a covalent bond in which 2 pairs of electrons are shared between 2 atoms
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double bond
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a covalent bond in which 3 pairs of electrons are shared between 2 atoms
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triple bond
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the greater the difference in electronegativity between bonded atoms the more ___ the bond has
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ionic character
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a term used to describe the uneven distribution of charge within a molecule
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polar
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polar molecules have ___ due to the uneven distribution of shared electrons between the bonded atoms
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partial charges
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give an example of a polar molecule
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water
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give an example of a nonpolar molcule
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carbon dioxide
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forces of attraction between molecules due to dipoles within molecules
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intermolecular forces
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why are intermolecular forces NOT considered chemical bonds?
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there is no interaction of valence electrons between molecules
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T/F: Intermolecular forces are much stronger than chemical bonds
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F
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the strongest intermolecular force
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hydrogen bonding
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the weakest intermolecular forces
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london dispersion forces
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___ strands are held together by hydrogen bonding
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dna
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generally liquids or gases at room temperature and have low melting points
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ionic compounds
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Electronegativity differences: 0.0
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pure covalent
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Electronegativity differences: 0.1-0.4
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non polar covalent
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Electronegativity differences: 0.41-1.7
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polar covalent
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Electronegativity differences: 1.7-→
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ionic
