Ch. 2 Flashcards
What is the difference between an ionic bond and a covalent bond?
An ionic bond involves one atom transferring/giving up an electron to another atom.
A covalent bond involves more than one atom sharing an electron.
Explain what electron shells are and how they are organized.
Electron shells are the designated orbitals surrounding atoms that electrons move in. The shells closest to the nucleus of the atom are the most tightly bound, and the electrons there are most strongly attracted to the positive charge of the nucleus. Most biological element atoms have four (out of 5) shells. Each shell is limited in the # of electrons it can contain. The limits on the maximum # of electrons each shell can contain are as follows: I: 1 / II: 8 / III: 8 / IV: 18 / V: 18. Atoms are most stable (not prone to radioactive decay) when the outermost electron shell is full. Shells fill outward (I -> V). If all shells are filled, atoms are stable and therefore chemically unreactive. Atoms that are not filled (e.g. the ones in living things) and therefore are reactive and inclined to form molecules via bonding (sharing, giving, or taking electrons) with other reactive atoms in order to become more stable.
How is atomic weight calculated?
Atomic weight is the # of protons + the number of neutrons in a given atom of a specified element.
What is a mole (mol)?
A mole is a measurement of mass equal to the # of grams of a given element that are required that obtain a total of 6 * 10^23 (Avogadro’s #) atoms of a given element.
This # is listed as the atomic/molecular mass on the periodic table. E.g. If carbon’s molecular weight is 12, 1 mole of carbon weighs 12 grams.
How are atomic numbers calculated?
The atomic # of an element is determined by the # of protons present at its atom’s nucleus. E.g. A hydrogen atom as 1 proton at its nucleus, therefore its atomic # is 1.
What charge do electrons have?
Negative
What charge do neutrons have?
Neutral
What charge do protons have?
Positive
What charge do whole atoms have, and why?
Whole atoms are electrically neutral, because the # of electrons surrounding the nucleus is equal to the # of protons within the nucleus.
What causes radioactive decay of an atom?
….
What determines the # of bonds an atom can make?
The # of electrons an atom must acquire or lose (by sharing or transferring) in order to fill its outer shell determines the # of bonds that the atom can make. E.g. Hydrogen has 1 electron, which means it has 1 of 2 maximum electron spots filled in its outermost (also happens to be innermost) electron shell. It can form only 1 additional to bond by sharing an electron in order to fill its outermost shell.
How does an ionic bond form?
When two atoms have a large electronegativity disparity and are both chemically reactive (with a need to give or receive/share electrons), the atom with the greater # of electrons transfers some of its electrons to the other atom, resulting in the “giver” atom having a net positive charge, and the “receiver” atom having a net negative charge - which then attracts them to each other. This type of bond is more likely to form when there is a large disparity between the electronegativity of the two atoms.
How many electrons are involved in a single covalent bond? What about a double covalent bond?
two (one electron from each atom), and four (two electrons from each atom), respectively.
What is hydrophobic force?
In an aqueous environment, force is generated by a pushing of non-polar surfaces out of the hydrogen bonded water network where they would otherwise physically interfere with the highly favorable interactions between water molecules.
What important role does hydrophobic force play in promoting molecular interactions?
It helps cellular membranes form because the lipid molecule’s C-H bond is is covalent and the Hydrogen has almost no net positive charge, so it cannot form effective hydrogen bonds to other molecules, resulting in lipids forming a barrier between internal and external aqueous environments.
