Describes how the universe expanded from an initial state of extremely high density and high temperature.Offers a comprehensive explanation for a broad range of observed phenomena

_______  means star

Formation of elements in the center of the star by nuclear reactions. Process by which elements are formed in the cores and shells of the stars through nuclear fusion reactions

suggests that stars form due to the collapse of the dense regions of an atomic cloud

Evolution of Stars

Evolution of Stars

stellar core that forms when cloud collapses and the fragments contract

Evolution of Stars

– protostar contracts and its temperature increases due to gravity; when gravitationalequilibrium is reached due to the release of positrons and neutrinos; contractions stop and main sequence staris formed

Evolution of Stars

Hydrogen is fused to helium in the core of main sequence star; pressure in the core decreases. Gravity squeezes the star to a point where helium and hydrogen burning occurs.Helium is converted to carbon in the core Hydrogen is changed to helium in the shell

Evolution of Stars

when most of helium in the core is carbon; rate of fusion decreases resulting in the squeezing ofstars. Star is depleted of its fuel. Over time, the outer material of the star is blown off into spaceOnly the hot inert carbon core will remainNo carbon fusion occurs here due to lack of mass

Evolution of Stars

carbon fusion occurs in massive stars where they have enough mass and there is anincrease in temperature and pressure

Star can fuse heavier elements in the core and in the shell around it.

 Oxygen from carbon fusion; ________________________

Star can fuse heavier elements in the core and in the shell around it

Magnesium from__________

Star can fuse heavier elements in the core and in the shell around it.

silicon from___________

Star can fuse heavier elements in the core and in the shell around it

iron from ________

Evolution of Stars

cores of red giant stars start to collapse when it can no longer produce enough pressure to resistgravityThis will lead to its explosion; releasing a large amount of energy and produces other elements heavier thaniron.

________ required high temperature and pressure

Cores of stars have very ______temperature and pressure

____________ burning in the core of stars produces energy in the stars

Same element (same number of proton)

Different number of neutrons- Have different atomic weight BUT same reactivity

involves changing atomic number of an element

- requires nuclear reactions with massive amounts of energy

- transformation of one element into another by a series of nuclear reactions

- elements are bombarded by protons and neutrons into it

also known as transuranic elements

- chemical elements with atomic numbers greater than 92

- produced by bombarding heavy atomic nucleus with smaller ionized particles via particle accelerator

– the way atoms bond with one another

one of the atoms in a bond has a stronger attractive force on the electrons in the link- electrons are pulled more towards that atom, resulting in small charge imbalance

determines polarity of a bond- expression of an atom’s tendency to attract electrons in a chemical bond- differences in electronegativities of atoms determine polarity

between 0.4 to 1.7

Greater than 1.7

Less than 0.4

electrons will be taken from the less electronegative element and spend their time orbiting themore electronegative element

is formed by bonded pair of atoms

Atom with higher EN becomes partial __________________ pole

Atom with lower EN becomes partial____________ pole

SYMMETRICAL =

ASYMMETRICAL =

Physical Properties of Covalent Compounds

Physical Properties of Covalent Compounds

temperature at which the vapor pressure and atmospheric pressure of liquid substances areequal

Physical Properties of Covalent Compounds

– temperature at which solid becomes liquid; solid and liquid phases exist in equilibrium

Physical Properties of Covalent Compounds

energy needed to increase the surface area by a unity amount

Physical Properties of Covalent Compounds

resistance of the liquid to flow

Physical Properties of Covalent Compounds

– pressure exerted by a substance in its gaseous state

Physical Properties of Covalent Compounds

rate at which a substance vaporizes; changes from liquid to gas)

Intermolecular Forces

Types of Intermolecular Forces

Force of attraction between charged particles and a polar molecule- Partially negative end of polar molecule will be attracted to the Cation (positively charged ion)- Partially positive end of polar molecule will be attracted to the Anion (negatively charged ion)

Types of Intermolecular Forces

Force of attraction in polar molecules like HCl- Dipole – unequal sharing of electrons between Hydrogen and Chlorine atoms in HCl- Molecules with permanent dipoles attract each other in dipole-dipole interaction- Positive end of one molecule attracts the negative end of other molecule- Results in partially positive pole in H and partially negative pole in Cl

Types of Intermolecular Forces

Link that exists between water molecules- Type of dipole-dipole interaction between the polar molecule Hydrogen and the highly electronegativeelements Flourine, Oxygen, and Nitrogen- The extremely electronegative elements cause hydrogen to become strongly positive in Hydrogen bond

Types of Intermolecular Forces

Can be found in all molecules- Weakest intermolecular force created by nonpolar molecule’s transient dipoles- As the molecular weight of the substance increases, so does the strength of the dispersion forces.

For reactions to occur, molecules, atoms, or ions must first collide; bump or touch each other with great force- Not all collisions are successful- Established how chemical reactions initiate change

minimum amount of energy for a chemical reaction to occur

– speed of certain chemical reactions

Rate of chemical reaction is directly proportional to the reactants’ concentration- Higher concentration of reactants = faster rate of reaction- Increasing reactant concentration ensures there will be more collisions and probability rate of effectivecollisions

Measure of the average kinetic energy of the molecule- Increased temperature of reactants = increase kinetic energy- Increasing temperature of reactants = increase number of collisions; providing energy to overcomeactivation energy

Exposed area of a substance- Increasing surface area = more particles are available for collision- Greater surface area = faster chemical reaction

Substances that increase reaction rate without being consumed in the chemical reaction- Allows reactions to occur with lower activation energy- Provides alternative reaction pathway; leading to higher rates of chemical reaction- Do not affect composition of the equilibrium; only affect the rate at which equilibrium is reached- Called “enzymes” in the body

reactant that is used up in the chemical reaction

reactant that is not used up in the chemical reaction

– amount of product obtained from a chemical reaction