CHAPTER 2 Flashcards
What is a chemical element?
- Elements that cannot be broken down into other substances
- There are 92 naturally occurring elements on earth
- you can combine elements and make compounds
Which 4 elements are most important for life on earth and why?
Oxygen - How cells break down the energy for cellular respiration
Carbon - Needed for photosynthesis
Hydrogen - Chemical compound for water (H2O)
Nitrogen - amino acids (proteins, DNA)
Give examples of trace elements.
Def: An element that is essential for the survival of an organism but is needed in only minimum quantities
Examples: Boron (B), Chromium (Cr), Iron (Fe), Iodine (I), Zinc (Zn), Fluoride (F), etc
Iodine deficiency - cause thyroid glands to enlarge which is called goiter
Iron deficiency - can cause anemia
Fluoride deficiency - can cause tooth decay
Describe atoms and subatomic particles
Atoms are the smallest chemical “units”
Subatomic particles:
Protons - positively charged ions
Electrons - negatively charged ions
Neutrons - have no charge
Protons + Neutrons: make the center part of an atom called the nucleus
Electrons: Orbit around the nucleus in energy “shells”
Define and describe atomic number
Tells you the number of protons in an element and the name of the element; protons share the same number of electrons if the element is neutral
Define and describe atomic mass
The number of protons + number of neutrons; in general the number of protons = number of neutrons
Define and describe radioactive isotopes
Isotopes: has the same amount of protons but different number of neutrons
Radioactive isotope:
unstable; the nucleus decays which emits radiation
Useful:
- biological tracers -> trace where a substance goes with radioactive markers
- carbon dating -> able to figure out the age of something since they decay overtime
Harmful:
- can cause damage on the cellular level; in your DNA causing mutations
Diagram an element given their atomic number and atomic mass
Ex:
Nitrogen; Atomic #7, Atomic mass 14, 3 unpaired electrons
Ex:
Carbon; Atomic #6, Atomic mass 12, 4 unpaired electrons
How does the number of electrons determine the properties of an element?
Elements orbit the nucleus in specific energy “shells”
=> the closest shell to the nucleus holds only 2 electrons
=> second and so on hold a total of 8 electrons
- elements with a full outer most shell are nonreactive and stable known as noble gases
- elements with one missing electron in its outermost shell wants to gain an electron
- elements with only one electron in its outermost shell wants to lose an electron
- when the outermost shell is full an element is stable
Define ionic bonds. Give an example of molecule and compound that are held together
Ionic bonds: are between atoms that donate an electron to another atom (between metal and nonmetal)
ex: Between Na+ and Cl-; Na gives an electron to Cl so they both have a full outermost shell -> NaCl
Define covalent bonds. Give an example of molecule and compounds that are held together.
Covalent bonds: between atoms that share electrons (nonmetals)
ex: CH4 -> Carbon has 4 empty spaces in its outermost shell; that’s where the 4 hydrogen atoms connect to the carbon atom
Define Hydrogen bonds. Give an example of molecule and compounds that are held together.
“Weaker bond, due to electrical attraction”
Hydrogen bonds: form a weak chemical bond when a positive hydrogen atom from one polar molecule that is attracted to a partially negative atom in another molecule
ex: between water molecules; makes water “sticky”
What are he four properties of water?
- Cohesion of water
- How water moderates temperature
- ice floating
- water solvent
What is cohesion of water? Why is it important?
Water molecules stick together due to weak hydrogen bonds that exist between the molecules
It is important because trees (plants) use this force to transport water through the roots to the leaves against the forces of gravity. It is also related to surface tension.
How does water moderate temperature? Why is it important?
Water has a high heat capacity -> if resists changing temperature when heat is added because the hydrogen bonds in water need to be broken first before it can be heated.
This is important because after a substance evaporates, the surface left behind cools down, like when humans sweat it cools down their skin; on a global level water moderated earth’s climate.
