CHEM EXAM REVIEW Flashcards
Democritus
Matter is made up of tiny indivisible particles called atoms
Aristotle
All matter is made up of 4 elements: earth, air, fire, and water
Philosophers vs scientists
Philosophers: come up ideas based on intuition and reason
Scientists: come up with ideas through experimentation using tools and technology
Dalton’s atomic theory
- Matter is made up of indivisible atoms called atoms
- Atoms of the same element elements are identical; atoms of different particles are different
- Chemical compounds are formed when atoms combine with each other
- Chemical reactions involve reorganization of atoms, but atoms can not be created or destroyed
Model: “billiard ball”- atom is a featureless sphere
Thomson’s experiment
-cathode ray tube
-ray filled with electrons
-reasoned that since atoms are electrically neutral, they must contain a positive charge
Model: plum pudding
Rutherford’s famous gold foil experiment
-positively charged alpha particle fire at a thin sheet of gold foil
-nucleus contains protons
-cloud of negatively charged electrons surround nucleus
Model: Beehive
chadwick
neutron is a neutral particle in nucleus
Bohr’s Experiment
-continuous spectrum: white light passing through prism
-emission spectrum: passing light from a hydrogen gas cathode ray tube through a prism
Bohr
-proposed electrons could move only in specific orbits around the nucleus
Bohr: planetary model
periodic law
when atoms are arranged in order of increasing atomic number, their properties show a recurrence and gradual change
atomic radius
measurement of the size of an atom
effective nuclear charge
-net force experienced by an electron in an atom due to the positively charged nucleus
Greater the effective nuclear charge, the smaller the atomic radius
-Radius decreases going across and increases going down the periodic table
In my own words: the more the electron orbits, the stronger the nuclear charge, pulling them close to the nucleus, making the radius small
-Cations always smaller than original atoms because they lose electrons
-Anions: always larger than their original atoms cause they gain electrons
Ionization energy
-quantity of energy required to remove an electron from an atom or ion
-Increases moving across and decreases moving down
In my own words: the further an electron is from a nucleus the easier it is to remove it because the inner electrons shield them from the positive charged nucleus
electron affinity
-Energy change that occurs when an electron is added to a neutral atom
-Increases moving across and decreases moving down
-Larger atoms have a weak attractive force from the nucleus and a strong repulsive for from the electrons
-In my own words: larger atoms have more electrons causing they to have a stronger repulsive force from the positive nucleus because the nucleus has a weaker attraction to more electrons
properties of ionic compounds
-form crystal lattice structure
-high melting and boiling points
-hard
-brittle
-conduct electricity
-electrolytes
non polar covalent vs polar covalent
-Nonpolar covalent bond: electrons are shared equally between atoms
-Polar covalent: electrons are not shared equally because one atom attracts them more strongly than the other atom
dipoles
-Separation of positive and negative charges in a region of space
-A polar bond will have a slightly positive end and a slightly negative end
-Represented using an arrow, arrow points toward more negative end
electronegativity
-ability of an atom in a molecule to attract shared electrons to itself
-increases going across decreases going down periodic table
-calculating the difference gives us information about the bond they will form
-draw arrow for polar bonds
intramolecular
chemical bond within a molecule
intermolecular
force occurs between molecules
london dispersion force
result from a random momentary non symmetrical electron distribution
-electrons from one molecule being attracted to the positive nucleus of an adjacent molecule
-all molecules experience it
-weakest
-strength increases with size, surface of contact or proximity
-low melting and boiling points
dipole-dipole
-electrostatic attraction caused when dipoles of polar molecules position their positive ends near each other
-only experienced by polar molecules
-strength increases with polarity, decreased distance between molecules
-intermediate melting and boiling points
hydrogen bonds
-strong dipole-dipole attraction
-occurs when a hydrogen atom bonded to a small highly electronegative atom (oxygen, nitrogen, or fluorine) is attracted to a partially negative atom on a nearby molecule
-strongest
-high melting and boiling points
-solid at room temp
-high surface tension
complete combustion vs incomplete combustion
Complete combustion
-oxygen supply is plentiful
-products are CO2 and H20
-very efficient because max amount of energy is produced
Incomplete combustion
-oxygen supply is limited
-products are CO2, H20, C, C0
-less efficient because less energy is produced
hydrocarbons
organic compounds made up of entirely of carbon and hydrogen atoms
Properties (ex: methane CH4, Propane C3H8)
Non polar
Insoluble in water
Can exist as gases, liquids, or solids at room temperature
Law of definite proportions:
elements in a compound are always present in the same proportion by mass
stoichiometry
study of mass and mole relationship between reacts and products in a chemical reaction
characteristic of solutions
Homogeneous: uniform composition throughout
Stable: solute particles do not settle over time
Can exist in various phases solid, liquid, or gas
disassociation
ionic compounds separate into individual ions in water
Ex. Na Cl -> Na+ (aq) + Cl- (aq)
hydration
water molecules surround and stabilize ions
miscibility and factors affecting it
ability of 2 liquids to mix and form a homogeneous solution
Factors affecting miscibility:
-Like dissolves like
-Intermolecular forces: hydrogen, dipole-dipole
surfactants
reduce surface tension between 2 substances, allowing them to mix
-Hydrophilic head: polar part that interacts with water
-Hydrophobic tail: nonpolar part interacts with oils and grease
concentration
amount of solute dissolved in a given quantity of solvent or solution
stock solution
highly concentrated solution used as a starting point to prepare more dilute solutions for practical applications
standard solution
solution prepared with precisely known concentration, often used for experiments and calibrations
strong acid vs weak acid
Strong acid: ionizes completely in water
Weak acid: substance only partially ionizes in water
titration, equivalence point, endpoint
-Titration: procedure use to determine the concentration of one solution
-Equivalence point: point in titration when neutralization is complete
-Endpoint: point in titration when indicator changes color (titration is complete)
Standard temperature and pressure
O degrees , 101.325 kPa
standard ambient temperature and pressure
25 degrees, 100 kPa
ideal gas law
hypothetical gas composed of no particles, have no size, travel in straight lines, have no attraction to each other. No such thing. We assume gases are ideal in order to simplify our equations to predict the behavior of real gases in most situations
Why do solids have a definite shape and volume?
Solids have a definite shape and volume because their particles are tightly packed in a fixed, orderly arrangement. The intermolecular forces in solids are strong, restricting the motion of particles to only vibrations around fixed positions. This rigidity prevents changes in shape or volume under normal conditions.
Why are gases relatively easy to compress while solids are virtually incompressible?
Gases are easy to compress because the particles in a gas are far apart and have large spaces between them, allowing them to be pushed closer together. In contrast, solids are virtually incompressible because their particles are already packed closely together in a fixed structure, leaving little to no space for compression.
Why do gases and liquids flow, while solids do not?
Gases and liquids flow because their particles can move past each other. In gases, particles are in constant, random motion with negligible attractive forces. In liquids, the particles are close but not fixed, allowing movement. Solids do not flow because their particles are locked in a rigid lattice, preventing relative movement.
Define STP and SATP
STP (Standard Temperature and Pressure): Defined as a temperature of 0°C (273.15 K) and a pressure of 1 atm (101.3 kPa).
SATP (Standard Ambient Temperature and Pressure): Defined as a temperature of 25°C (298.15 K) and a pressure of 1 bar (100 kPa).
(b) Explain why scientists have defined two sets of standard conditions.
(c) Which standard is most frequently used, and why?
SATP is more frequently used because it represents conditions closer to real-world temperatures and pressures encountered in laboratories and daily life, making it more practical for most applications.
(b) Explain why scientists have defined two sets of standard conditions.
STP is used for calculations requiring precise and controlled baseline conditions, often in scientific research. SATP reflects conditions closer to everyday ambient environments, making it more practical for general chemical and industrial applications.
(c) Which standard is most frequently used, and why?
SATP is more frequently used because it represents conditions closer to real-world temperatures and pressures encountered in laboratories and daily life, making it more practical for most applications.
What happens to a sample of matter cooled to absolute zero?
At absolute zero (0 K or -273.15°C), the motion of particles theoretically ceases entirely. In this state, a substance would have no thermal energy, and all particles would occupy their lowest energy state. In reality, absolute zero is unattainable, but approaching it leads to phenomena like superconductivity and superfluidity.
