The mass number of an atom is 15, and its atomic number is 7. The atom probably has
8 neutrons in the nucleus. The atomic number (7) gives the number of protons, and the mass number is the number of protons plus neutrons
Which statement is true of atoms?
Electrons determine the atom's size. With electrons on the surface, atoms repel one another when they come too close. Thus, electrons determine the space that an atom occupies.
Dr. Jones says an atom has 3 electrons in the first shell and four electrons in the second shell. Someone should tell Dr. Jones that
the first shell shouldn't have 3 electrons.The first shell can only have 0, 1, or 2 electrons
Which statement is true of the energy levels of electrons in shells
The valence shell has higher energy than other occupied shells. The outer occupied shell is the valence shell, and outer shells hold electrons at higher energy than inner shells
An orbital is dumbbell-shaped. Which statement is most likely true
Only the second and higher shells have dumbbell-shaped orbitals. Each orbital can hold just two electrons, and the electrons move in unknown paths such that both electrons can be in one lobe at one moment, and in opposite lobes at the next moment
Two atoms always represent the same element if they have
the same number of protons. The number of protons defines a chemical element
An atom has 6 electrons, 6 protons, and 6 neutrons. You can tell that this atom belongs to the element _____ because _____________________
C; it has 6 protons.
An atom has 8 protons, 8 neutrons, and 8 electrons. Another isotope of the same element might have
10 neutrons. Isotopes have the same number of protons; different numbers of neutrons
Radioactive decay is likely to occur when
an atom has too many neutrons. The atomic nucleus becomes unstable if the ratio of protons to neutrons is too far from unity
Which model most accurately represents the current view of the structure of the atom
Covalent bonds hold atoms together because they
fill shells without giving atoms much charge, bring electrons closer to protons
An atom's atomic number is 7. Its valence is most likely
3. The neutral atom has 7 electrons. Two electrons fill the first shell, and 5 go into the second (valence) shell. The atom needs 3 more electrons to fill the valence shell.
By making two covalent bonds, an O atom (with 8 protons) fills its valence shell. Why does the atom's charge stay close to zero
Shared electrons aren't always near oxygen
Two C atoms form a double bond. Each C is bound to two H atoms. Which statement is true
All the atoms lie in a plane
To fill the valence shell, an electrically neutral, unbonded atom with atomic number 8 must add
Which answer helps to explain why carbon atoms tend to make 4 covalent bonds?
The valence shell needs 8 electrons.
An electrically neutral molecule has the formula C3H4O2N. If the carbon atoms form the usual number of bonds, how many covalent bonds will each hydrogen atom have with other atoms in the molecule?
Which answer correctly ranks the atoms in terms of decreasing electronegativity (the highest electronegativity first)
Dr. Haxton says the O-O bond is polar and the C-C bond is nonpolar. A good student would say
Wrong again, Ralph. Both bonds are nonpolar
Which item is based on differences in electronegativity between atoms
the organization of phospholipids into bilayers, The pairing of bases in DNA, The tertiary folding of proteins
A cation with two units of charge has 10 neutrons and 8 protons. The ion also has
6 electrons. The part with the two units of + charge is a cation; the part with the unit of - charge is an anion
True or false: Ions may form by transferring an atomic nucleus (with or without electrons) to another molecule
When chemists and biologists want to show how atoms are bonded in a molecule, they usually use a
Polar attractions are
forces between atoms with partial charges, weaker than covalent bonds, important because they are numerous.
Dr. Haxton told his class that a water molecule can make 4 hydrogen bonds, all of them in the same plane as the three atoms. What would a good student reply
Wrong! Two hydrogen bonds are not in the plane of the atoms
Which statement is part of the explanation for water's high cohesion
Oxygen has four valence orbitals, Oxygen is much more electronegative than hydrogen.
Which answer helps to explain how many hydrogen bonds a water molecule can form
Oxygen's valence shell has four orbitals
Which statement must be mentioned in explaining why amphipathic molecules line up at a water surface
Polar groups attract one another
Which statement is true of water's tensile strength?
It results from hydrogen bonding, It helps to pull water through plants, It involves both cohesion and adhesion
Water has surface tension because ...
hydrogen bonds between surface water molecules resist being stretched.
Which of the following helps most to explain why water has a high specific heat?
A water molecule can make 4 hydrogen bonds.
describes the alpha-helices and beta sheets that are formed by hydrogen bonding between backbone atoms located near eachother in the poly peptide chain
a protein folds into a compact 3D shape stabilized by interactions between side chain R-groups of amino acids
result of 2 or more protein subunits assembling to form a larger biologically active protein complex
an enzyme is considred specific because
it's ability to recognize the shape of a particular molecule
has a structure that is so similar to a substrate that it can bond to the enzyme just like a substrate
forms a covalent bond with an amino acid side group within the active site, which prevents that substrate from entering the active site, or prevents catalytic activity