Chapter 2 - The Chemical Context of Life
The atomic nucleus is made up of what? and is surrounded by what?
- The atomic nucleus is comprised of protons and neutrons; the protons are what give the nucleus a positive charge. - The positively charged nucleus is surrounded by negativity charged electrons.
Potential energy & energy levels in a atom's electrons
- The electrons of an atom have potential energy due to their distance from the nucleus It takes work to move a given electron farther away from the nucleus, so the more distant an electron is from the nucleus, the greater its potential energy - an electron's potential energy is determined by its energy level (which is then correlated with its distance from the nucleus)
Chemical reactions - what is the fundamental process driving these reactions and how is matter conserved?
A chemical reaction is a process in which one or more substances, also called reactants, are converted to one or more different substances, known as products. The making and breaking of chemical bonds, leading to changes in the composition of matter, are called chemical reactions. Matter is conserved in a chemical reaction: Reactions cannot create or destroy atoms but can only rearrange (redistribute) the electrons among them.
radioactive isotope
A radioactive isotope is one in which the nucleus decays spontaneously, giving off particles and energy. When the radioactive decay leads to a change in the number of protons, it transforms the atom to an atom of a different element. - used in radiometric dating
hydrogen bond
A type of weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule. When a hydrogen atom is covalently bonded to an electronegative atom, the hydrogen atom has a partial positive charge that allows it to be attracted to a different electronegative atom nearby.
All atoms of a particular element have the same number of [what] in their nuclei? What differs?
All atoms of a particular element have the same number of protons in their nuclei. Some atoms have more neutrons than other atoms of the same element and therefore have greater mass.
Are chemical reactions reversible? What factors affect reverse reactions and why?
All chemical reactions are theoretically reversible, with the products of the forward reaction becoming the reactants for the reverse reaction One of the factors affecting the rate of a reaction is the concentration of reactants or products. The greater the concentration of reactant molecules, the more frequently they collide with one another and have an opportunity to react and form products.
Define Chemical bonds; what are the strongest chemical bond types?
An attraction between two atoms resulting from a sharing or transferring of outer-shell electrons. The strongest kinds of chemical bonds are covalent bonds and ionic bonds in dry ionic compounds.
An electron can move from one main energy level to a higher one only by
An electron can move from one shell to another, but only by absorbing or losing an amount of energy equal to the difference in potential energy between its position in the old shell and that in the new shell. - if the electron loses energy, it'll fall back into a lower shell and that lost energy is released to the environment as heat.
8. What coefficients must be placed in the following blanks so that all atoms are accounted for in the products? C6H12O6 S _________ C2H6O + _________ CO2 (A) 2; 1 (B) 3; 1 (C) 1; 3 (D) 2; 2
Answer: (D) 2; 2
4. Which statement is true of all atoms that are anions? (A) The atom has more electrons than protons. (B) The atom has more protons than electrons. (C) The atom has fewer protons than does a neutral atom of the same element. (D) The atom has more neutrons than protons.
Answer: (A) The atom has more electrons than protons.
TEST YOUR KNOWLEDGE SECTION: 1. In the term trace element, the adjective trace means that: (A) the element is required in very small amounts. (B) the element can be used as a label to trace atoms through an organism's metabolism. (C) the element is very rare on Earth. (D) the element enhances health but is not essential for the organism's long-term survival.
Answer: (A) the element is required in very small amounts.
6. We can represent atoms by listing the number of protons, neutrons, and electrons—for example, 2p+, 2n0, 2e- for helium. Which of the following represents the 18O isotope of oxygen? (A) 7p+, 2n0, 9e- (B) 8p+, 10n0, 8e- (C) 9p+, 9n0, 9e- (D) 10p+, 8n0, 9e-
Answer: (B) 8p+, 10n0, 8e-
3. The reactivity of an atom arises from: (A) the average distance of the outermost electron shell from the nucleus. (B) the existence of unpaired electrons in the valence shell. (C) the sum of the potential energies of all the electron shells. (D) the potential energy of the valence shell.
Answer: (B) the existence of unpaired electrons in the valence shell.
7. The atomic number of sulfur is 16. Sulfur combines with hydrogen by covalent bonding to form a compound, hydrogen sulfide. Based on the number of valence electrons in a sulfur atom, predict the molecular formula of the compound. (A) HS (B) HS2 (C) H2S (D) H4S
Answer: (C) H2S
5. Which of the following statements correctly describes any chemical reaction that has reached equilibrium? (A) The concentrations of products and reactants are equal. (B) The reaction is now irreversible. (C) Both forward and reverse reactions have halted. (D) The rates of the forward and reverse reactions are equal.
Answer: (D) The rates of the forward and reverse reactions are equal.
2. Compared with 31P, the radioactive isotope 32P has: (A) a different atomic number. (B) one more proton. (C) one more electron. (D) one more neutron.
Answer: (D) one more neutron.
Oxygen has an atomic number of 8 and a mass number of 16. Thus, what is the atomic mass of an oxygen atom? A) exactly 8 grams B) exactly 8 daltons C) approximately 16 grams D) approximately 16 daltons E) 24 amu (atomic mass units)
Answer: D) approximately 16 daltons
Titanium has an atomic number of 22. How many protons, neutrons, and electrons are in an isotope of titanium with mass number of 48? a) p = 22, n = 26, e = 22 b) p = 11, n = 26, e = 11 c) p = 11, n = 11, e = 70 d) p = 11, n = 22, e = 48 e) p = 22, n = 22, e = 48
Answer: a) p = 22, n = 26, e = 22
What types of bond is very prevalent in lipids and gives lipids their hydrophobic properties? A) polar covalent B) nonpolar covalent C) strong ionic D) weak ionic E) hydrogen
Answer: b) nonpolar covalent
Isotope
Atoms of the same element (same number of protons) that have different numbers of neutrons - Isotopes are important as tracers, as they will label atoms, you can follow these atoms by measuring the decay
Define Covalent bonds
Bonds created by sharing electrons with other atoms. - two or more atoms held together by covalent bonds constitute a molecule - Each atom that can share valence electrons has a bonding capacity corresponding to the number of covalent bonds the atom can form
Define electronegativity and how it determines the attraction of a particular atom for the electrons of a covalent bond
Electronegativity describes the tendency of an atom or a functional group to attract electrons toward itself. The more electronegative an atom is, the more strongly it pulls shared electrons toward itself.
What are essential elements? What are the four elements that make up 96% of life?
Essential elements that an organism needs to live a healthy life and reproduce. oxygen (O), carbon (C), hydrogen (H), and nitrogen (N)—make up approximately 96% of living matter.
Ionic bonds
Ionic bonds are formed when one or more electrons are transferred from one atom to another. After this transfer occurs the atoms become ions. After this transfer, the ion that loses an electron forms a positive charge [becoming a cation], while the ion that gains an electron forms a negative charge [becoming an anion]. Because of their opposite charges, cations and anions attract each other; this attraction is called an ionic bond.
Matter - Elements and Compounds
Matter: Anything that has mass and takes up space. Elements: is a substance that cannot be broken down to other substances by chemical reactions. Compound: A compound is a substance consisting of two or more different elements combined in a fixed ratio. (ex table salt)
nonpolar covalent bond and polar covalent bond
Nonpolar covalent bond: A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity (or two of the exact same atom) Polar covalent bond: A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive.
Polarity - how is it determined and what is its significance
Polarity: Molecules having uneven distribution of charges Determined by the electronegativity of an atom Significance: determines the bonding type of atoms together - and then the overall polarity of a molecule is determined by the shape (ex dipole moments)
Van der Waals interactions
Spontaneous weak attractions between molecules or parts of molecules that result from transient local partial charges.
The chemical behavior of an atom is determined by [what]?
The chemical behavior of an atom is determined by the distribution of electrons in the atom's electron shells (mainly the valence electrons in it's outermost shell) - The reactivity of an atom arises from the presence of unpaired electrons in one or more orbitals of the atom's valence shell.
molecular shape and its significance
The geometric shape formed by atoms bonded to the central atom in a molecule Molecular shape is crucial: It determines how biological molecules recognize and respond to one another with specificity. Biological molecules often bind temporarily to each other by forming weak interactions, but only if their shapes are complementary
electron orbitals
The three dimensional space where an electron is found 90% of the time - each concentric circle represents only the average distance between an electron in that shell and the nucleus. - each electron shell contains electrons at a particular energy level - No more than 2 electrons can occupy a single orbital
If an atom has a neutral electrical charge, what can yo infer from this? also what does atomic number tell us?
Unless otherwise indicated, an atom is neutral in electrical charge, which means that its protons must be balanced by an equal number of electrons. *Atomic number tells us the number of protons and also the number of electrons if the atom is neutral.
chemical equilibrium
When the forward and reverse reactions occur at the same rate, and the relative concentrations of products and reactants stop changing. This is a dynamic equilibrium; reactions are still going on in both directions, but with no net effect on the concentrations of reactants and products Equilibrium does not mean that the reactants and products are equal in concentration, but only that their concentrations have stabilized at a particular ratio.
How do you find the number of neutrons?
mass number (total # of protons + neutrons in nucleus)- atomic number (# of protons)
potential energy
stored energy that results from the position or shape of an object (ex water moving down a hill)
