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MED 103- BIOLOGY I > 5. VALENCE ELECTRONS > Flashcards

5. VALENCE ELECTRONS Flashcards

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1
Q
  1. What are valence electrons?
A
  • the electrons in the outermost shell
  • they determine the chemical behaviour of an atom
  • they are involved in the chemical bonds between atoms
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2
Q
  1. What do atoms do with their valence electrons?
A
  • they wither share or transfer them
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3
Q
  1. What is the result of this transfer or sharing of valence electrons?
A
  • chemical bonds form between atoms
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4
Q
  1. How many electrons can the second and the third shell of an atom hold?
A
  • up to 8 electrons
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5
Q
  1. How many electrons can the first shell of an atom hold?
A
  • up to 2 electrons
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6
Q
  1. What are Covalent Bonds?
A
  • they are the sharing of electrons between atoms
  • it is the sharing of a pair of valence electrons by two atoms
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7
Q
  1. What are Ionic Bonds?
A
  • they are the transfer of electrons from one atom to another
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8
Q
  1. What usually holds an electron in its orbital?
A
  • its attraction to the proton in the nucleus
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9
Q
  1. What happens when two atoms approach each other?
A
  • the electrons in the orbital atoms are attracted to the protons in the nucleus of the other atom
  • this leads to the sharing of electrons
  • resulting in a covalent bond forming
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10
Q
  1. What does a molecule consist of?
A
  • 2 or more atoms held together by covalent bonds
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11
Q
  1. What is a single bond?
    Provide an example.
A
  • the sharing of one pair of valence electrons

EG: two hydrogen atoms share one single covalent bond

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12
Q
  1. What is a double bond?
    Provide an example.
A
  • it is the sharing of two pairs of valence electrons

EG: two oxygen atoms share one double covalent bond

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13
Q
  1. What is the definition of Electronegativity?
A
  • it is the tendency of an atom to attract electrons towards itself
  • it is affected by the atomic number of the atom
  • it is affected by the distance of the atom’s valence electrons from the charged nucleus
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14
Q
  1. What is the result of having a more electronegative atom?
A
  • it pulls the shared electrons towards itself more strongly
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15
Q
  1. Along which aspects of the periodic table does the electronegativity increase?
A
  • it increases alone the period (from left to right)
  • it increases up the group (from bottom to top)
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16
Q
  1. What are the electronegativities of the atoms like in a non-polar covalent bond?
A
  • these atoms have similar electronegativities
  • this allows them to share the electrons equally
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17
Q
  1. What are the electronegativities of the atoms like in a polar covalent bond?
A
  • the atoms have different electronegativities
  • this results in them sharing electrons unequally
18
Q
  1. What is an example of a Polar Covalent bond?
A
  • a water molecule (H2O)
19
Q
  1. What can be said about the electronegativity between oxygen and hydrogen?
A
  • Oxygen (O) is more electronegative than hydrogen (H)
  • the shared electrons will be pulled more towards the oxygen atom
20
Q
  1. What does this electronegativity difference in the water molecule result in?
A
  • this forms a partially negative charge on the oxygen atom
  • it forms partially positive charges on the hydrogen atoms
  • this forms a polar molecule
  • these two partial charges attract one another
  • this leads to the 2 single covalent bonds forming
21
Q
  1. What are Ionic bonds?
A
  • they are the electrons that are transferred from one atom to another
  • they result in an electrostatic attraction between the atoms
  • it is an attraction between cations and anions
22
Q
  1. What does this transfer of electrons create?
A
  • ions
23
Q
  1. What are ions?
A
  • they are charged atoms
  • they have fewer or more electrons than usual
  • they are not neutral
24
Q
  1. What are positively and negatively charged ions called?
A
  • Positively charged Ions = Cations (more protons)
  • Negatively charged Ions= Anions (more electrons)
25
Q
  1. What are Ionic Compounds known as?
A
  • salts
  • these can form crystals
  • they usually consist of a metal and a non-metal that are ionically bonded together
26
Q
  1. What are the 2 examples of strong chemical bonds?
A
  • Covalent Bonds
  • Ionic Bonds
  • these are bonds between atoms
27
Q
  1. What are the 2 examples of weak chemical bonds?
A
  • Hydrogen bonds
  • Van der Waals Interactions
  • these are the bonds between atoms within molecules, or between molecules
28
Q
  1. What are Hydrogen bonds?
    Provide an Example.
A
  • they are bonds between a hydrogen atom (H) and the electronegative atoms of nitrogen, oxygen and fluorine molecules
  • these bonds are covalent bonds
  • they are found between DNA nucleotides
  • it is an interaction between neighbouring molecules

EG: the hydrogen bonds found between hydrogen atoms and oxygen atoms in a water molecule

29
Q
  1. How does the Hydrogen bond between the Hydrogen atom in a water molecule and the Nitrogen atom in ammonia occur?
A
  • there is an attraction between the partially positive charge on the hydrogen atom of the water molecule

AND

  • the partially negative charge on the nitrogen atom of ammonia
30
Q
  1. What are Van Der Waals interactions?
    Provide an example.
A
  • they are attractive forces
  • they are NOT bonds
  • they develop between molecules or between atoms of a molecule
  • they occur when temporarily positive and negative regions of molecules attract each other
  • they are weaker than Hydrogen bonds

EG: they are found in polypeptide tertiary structures
: this is also known as protein folding

31
Q
  1. What is the role of weak Chemical Bonds?
    (such as hydrogen bonds and Van Der Waals
    interactions)
A
  • they reinforce the shapes of large molecules
  • they help neighbouring molecules adhere to each other
32
Q
  1. Why is the precise shape of the molecule important to its function in the living cell?
    (EG: the shape of a protein)
A
  • the shape of the molecule determines the function of the molecule
  • the molecule cannot function without its proper shape
33
Q
  1. Where do covalent bonds form?
A
  • between atoms of the same element
  • between atoms of different elements
34
Q
  1. What is a molecule?
A
  • they consist of two or more atoms held together by covalent bonds
  • EG: H2, H2O
35
Q
  1. What is a compound?
A
  • it is a combination of two or more DIFFERENT elements
  • EG: H2O
36
Q
  1. Are molecules always compounds?
A
  • NO
  • molecules are not always compounds
  • compounds are always molecules
  • molecules can consist of the same element
  • compounds cannot consist of the same elements
37
Q
  1. What are chemical reactions?
A
  • they are the breaking and making of chemical bonds
38
Q
  1. What are the starting chemicals of a chemical reaction called?
A
  • REACTANTS
39
Q
  1. What are the final molecules of a chemical reaction called?
A
  • PRODUCTS
40
Q
  1. What is Photosynthesis an example of?

Name the:
70.1: Reactants
70.2: Products

A
  • a chemical reaction

70.1: CO2 + H2O (Carbon Dioxide and Water)
70.2: O2 + C6H12O6 (Oxygen and Glucose)

41
Q
  1. Read through the summary.
    Does everything make sense?
A
  • yes

MED 103- BIOLOGY I (53 decks)

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