Chemistry Flashcards
What 3 parts make up an atom?
- Protons
- Neutrons
- electrons
Where are electrons found?
In orbitals going around the nucleus
How many can electrons can each electron hold?
- 2 in the first
- 8 in all thereafter
How does the periodic table arrange atoms?
by the number of protons, also arranges them by properties
What is the ratio of protons to electrons in an uncharged atom?
1:1
What are the valence electrons?
the ones in the outermost shell of the atom
Why are valence electrons important?
They determine how an atom interacts with others
What makes an atom to be in it’s most stable state?
full outer shell
What is the name for the process which causes an atom to lose electrons?
oxidation - forms a cation
What is the name of the process which causes an atom to gain electrons?
reduction - forms anions
What is a molecule?
A group of atoms held together in a stable assoication
What is a compound?
A molecule containing more than one type of element
What allows an ionic bond to form?
Large difference in electrongegativity, (different charge)
What makes a covalent bond stronger?
the number of bonds
single < double < triple…
What is a true covalent bond?
A covalent bond with no difference in electronegativity
What does an electronegativity difference of >1.8 mean for bonding?
Ionic bonding
What does an electronegativity difference of 1.8>x>0.4 mean for bonding?
Polar covalent bond
What does an electronegativity difference of <0.4 mean?
nonpolar covalent bond
What limits chemical reactions?
- temperature
- concentration
- catalyst
- free energy
What kind of bonding is present in water?
polar covalent and hydrogen
What happens in hydrogen bonding?
A very high electronegativity difference causes the molecules to form greater inter-particle interactions with other molecules
What are the physical properties of water?
- high specific heat capacity
- high heat of vaporization
- high specific latent heat
- high surface tension
What do the terms hydrophillic and hydrophobic mean?
Hydrophillic - bonds readily with water
Hydrophobic - does not bond with water - is imiscible with it
Is water better at dissolving charged (ionic) or non-charged molecules?
ionic
What is solubility?
A measure of how much solut can be dissolved in a solvent
What effects solubility?
Temperature and pressure
How does temperature effect solubility?
solubility of most gases decrease with increasing temperature
solubility of solids increase with increasing temperature
What is Henry’s law?
The amount of dissolved gas is proportional to its partial pressure above the liquid
X(aq) = K*Px
How can solubility be related to an equilibrium reaction?
- salt is put into water and begins dissolving
- salt continues to dissolve; however dissolved ions will also precipitate. Because the salt dissolves faster than its ions precipitate, the net movement is towards dissolution
- the rate of dissolution will eventually equal te rate of preciptiation. Solution is in equilibrium - ions will continue to dissolve and precipitate
What is the equation for molarity?
= [moles of solute/ litres of solution]
What does a mole show?
The number of molecules in a given mass
n = m/gfm
What does GFM stand for?
gram formula mass
What is the equation for normality?
N = equivalent of solute/1L of solution
What is the equilibrium constant?
The equilibrium expression for a reaction of constant temperature
Keq = [C]^c[D]^d/[A]^a[B]^b
the objects in [] represent the molar concentration, molarity, moles per litre
Products over reactants, each to the power of their coefficients
Precicts the predominant direction of the reaction
What does the equilibrium equation relate?
The concentration of reactants and products
What is Le Chatelier’s principle?
“When an equilibrium system is subjected to a change in temperature, pressure or concentration of a reacting species, the system reacts in a way that partially offsets the change while reaching a new state of equilibrium”
What doe Le Chatelier’s principle mean?
Any stress placed on a system in equilibrium will cause the system to shift to minimise the effect of the stress
What defines the amount of a gas in liquid?
Henry’s law
What is the unit of K if the gas concentration is in Moles/ Litre?
Mole/ litre/ atm
What is biochemical oxygen demand?
a measure of water pollution
What does biological oxygen demand measure?
How much dissolved oxygen is consumed as microbes/ bacteria break down organic matter
What does high BOD indicate?
that levels of dissolved oxygen will fall, with potentiall dangerous implications for biodiversity
What causes high BOD?
high levels of organic pollution
Microbial activity uses up O2
What is an acid?
A chemical that releases H^+1 ions
What is a base/ alklai?
a chemical that accepts H^+1
What is a buffer?
A chemical that accepts/ releases H^+1 ions as necessary to keep pH constant
What is the definition of an acid?
Anything that produces hydrogen ions in a water solution
What is the definition of a base?
Anything that produces hydroxide ions in a water solution (OH^-)
What are some common acids?
- Citrus fruits
- Aspirin
- Vitamin C
- Vinegar
- hydrochloric acid
What are some common bases?
- detergents
- ammonia based cleaners
- sodium hydroxide
What can the strength of an acid be expressed by and what does it mean?
equilibrium - the equilibrium constant can be found
K <1 is a weak acid
What does a buffer solution usually consist of?
A weak acid and a salt that releases additional A^- ions
A salt procides a high cocentraion of A^- ions
What is the usual equation for a weak acid?
HA + H2O –> H3O^+ + A^-
How do you remove metal ions from a solution?
precipitate them as a metal hydroxide
How do we precipitate metals?
- Raise pH with a common alklaine material
- metals bcome insoluble
- precipitate them
What is the drinking water standard for alkilinity?
there isn’t one
What is alkalinity?
The capacity to neutralise an acid, hence why there is no drinking water standard
What is hard water?
The concentration of calcium carbonate
How is the contents of hard water precipitated?
As a result of le Chatelier’s principle, it can have hug costs and loss of energy
What causes hard water?
Ca^2+, Mg^2+, Fe^2+, Mn^+