Elements, Atoms, and Compounds
Chemical Bonds
Chemical Bonds pt. 2
Waters Life Supporting Properties
100
How are trace elements (elements that are essential for life but only needed in small amounts) helpful?
-prevent disease
-In food: preservation, more nutrition, look more appealing
100
Describe a covalent bond and a hydrogen bond. Explain their characteristics (HINT: Are they weak or strong bonds)
-Covalent bond: A strong chemical bond in which two atoms share one or two pairs of valence electrons between them
-Hydrogen bond: A weak chemical bond forms 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
100
What is the difference between polar and nonpolar covalent bonds?
Polar: One atom is more electronegative than the other resulting in electrons being pulled closer to the more electronegative atom
Nonpolar: Atoms have similar electronegativity so electrons are shared equally
100
What is the difference between cohesion and adhesion?
Cohesion: The tendency of molecules of the same kind to stick together (often by hydrogen bonds)
Adhesion: The clinging of one substance to another
200
Describe an atom and its elements
-an atom is the smallest unit of matter that still retains the properties of an element
-Neutrons (no electrical charge, in nucleus)
-Protons (single positive charge, in nucleus)
-Electrons (single negative charge, move around nucleus)
200
What enables other water molecules to hydrogen bond to one another?
Due to polarity (The oxygen of one water molecule is attracted to the hydrogen of another)
200
Is water (H2O) a polar or a nonpolar molecule and what type of bonds does the oxygen have with the hydrogen?
-water is a polar molecule because oxygen is more electronegative than hydrogen which forms polar covalent bonds
200
How does thermal energy connect with evaporative cooling? Name an example.
-Thermal energy: energy associated with the random movement of atoms and molecules
-Evaporative cooling: When a substance evaporates
300
What is the difference between an element and a compound?
-Element: a substance that cannot be broken down into other substances by ordinary chemical means
-Compound: a substance consisting of two or more different elements combined in a fixed ratio
300
What makes some elements more stable and unstable than others
-Stable Elements have a full valence shell
-Unstable Elements need to lose or gain electrons to have a complete valence shell so they're more likely to interact with other elements
300
Describe an ion
an atom or molecule with an electrical charge resulting from gain or loss of one or more electrons
300
How is cohesion related to surface tension? (HINT: Think of water properties)
Surface tension: a measure of how difficult it is to break the surface of a liquid
Molecules like water that are cohesive with each other and hydrogen bonds form a tension on the surface of a liquid making the top like an invisible film.
400
What are the differences between atomic number, mass number, and atomic mass?
-atomic number: The unique number of protons
-mass number: The sum of protons and neutrons
-Atomic mass: Is approximately equal to its mass number
400
How many covalent bonds can carbon form and why?
-4 bonds because its outer shell isn't full
-The number of covalent bonds an atom can form depends on the number of electrons needed to fill its valence shell
400
How are the ions in a crystal of table salt (NaCl) held together?
-opposite charges attract. The positively charged Na ions and negatively charged Cl ions are held together with ionic bonds
-Na has a charge of positive 1
-Cl has a charge of negative 1
400
Why is water less dense as a solid than a liquid?
-When water freezes, its molecules spread out and make hydrogen bonds with its neighbors, forming a crystal lattice compared to liquid water the molecules are tightly packed.
-The ice has fewer molecules than liquid water making it less dense.
500
_____ of an element have the same number of protons but different numbers of neutrons
Isotopes
500
Explain what an ionic bond is?
The actual transfer of an electron between atoms which forms a chemical bond resulting from the attraction between oppositely charged ions
500
This is a chemical reaction
aA + bB → cC + dD
What are A and B? What are C and D?
Reactants and products
500
What is a pH scale used for?
to describe how acidic or basic a solution is