Resumen Science I Trimestre II Parcial
1. Definitions:
Element: pure substance that can’t be separated into simpler substances by chemical or
physical methods. Unique characteristic: can’t be broken down into smaller particles or
substances.
Atom: basic particles of elements. Elements are made from atoms; atoms aren’t made of
elements.
Chemical bond: force of attraction between 2 atoms that holds them together. Ex: H2O
Molecule: particle of a compound; formed when atoms of 2 or more elements join together.
Compound: pure substances composed of 2 or more elements that are chemically combined;
elements combine reaction with one another.
Chemical Formula: is the fundamental unit of an element. The symbols for the elements are
written together; numeral subscripts indicate the ratio in which the atoms are combine. The
subscript 1 is understood and omitted.
Ex. NH3, NaCI
Ratio: is the amount of elements in a compound. Element join in a specific ratio (amount of the
element), according to their mass to form a compound. Ex. 16g
Mixture: combination of 2 or more substances that are not chemically combined. (Physical
change: so each substance has the same chemical makeup that it has before forms). Compound
of mixtures don’t have to mix in definite ratios. Ex: granite (mix different materials) different
ratios of minerals give granite colors but is always called granite.
Heterogeneous mixture: different components can be seen as individual substances, particles
visible. Ex. Pizza, oil and water, gallo pinto.
Homogeneous mixtures: same composition through any one region of a mixture has the same
ratio of a substance as any other region, compounds can’t be seen as individual identifiable
entities mixed as much finer level, not readily distinguish. Ex. Water with salt
Solution: appears to be a single substance. Process in which particles of substance separate and
spread evenly through a mixture is known as dissolving.
Suspension: is a mixture in which particles of a material are dispersed throughout a liquid or a
gas but are large enough that they settle out.
Colloids: Is a mixture in which the particles are spread throughout but are not large enough to
settle out
2. Differentiate between a homogeneous and a heterogeneous mixture and provide examples.
Homogenous Mixtures
Have the same composition throughout.
Heterogeneous Mixtures
Different components can be seen as individual
substances.
Any region of the mixture has the same ratio of We can almost separate the components with our
substance as any other region
eyes
The components can´t be seen as individual
The particles are visible
indentifiable entities
3. Differentiate between colloids, suspensions, solutions.
Solutions
Uniformly disersed
Single phase
Small paricles
Can't scatter light
Suspensions
More or less dispersed
More phases
Large particles that settle out
Scatter or block light
Colloids
Intermediate dispersed
More phases
Intermediate particles
Scatter light
Examples:
Solutions: soft drinks, gasoline, tap water, steel, and alloys.
Suspensions: blood
Colloids: fog, ketchup,
milk
4. Differentiate between a pure substance and a mixture.
Pure substances: material that consist of only a single element or a single compound.
Pure (relative term): nothing is 100% pure, maybe 99.999% without a lot of imparities.
Classification of elements:
Physical properties:
-Hardness
-Melting point
-Density
Chemical properties:
-Reactivity
-Flammability
Classification of compounds:
Physical properties:
-Melting point
-Boiling point
- Density
-Color
Chemical properties:
-Reaction with other elements
-Reaction to heat
-Reaction to light
-Flammability
Compound
Table Salt (NaCl)
Water (H2O)
Sugar (C6H12O6)
Carbon Dioxide (CO2)
Baking Soda
Element in the compound
Sodium + Chlorine
Water + Oxygen
Hydrogen + Carbon + Oxygen
Carbon + Oxygen
Sodium + Hydrogen + Carbon + Oxygen
3 major categories
Properties
appearance
conductivity
(heat electric)
malleable
(sheets)
ductile
(wires)
Brittle
metal non metal
shiny dull
good poor
metaloids
some are shiny
some do
yes
no
yes
no
No
Yes
some are some
what malleable
some are some
what ductible
Some are
Metals: Lead, Tin, Copper, except of Mercury it is liquid
Non metals: Iodine, Sulfur, Neon
Metaloids: Boron, Silicon, Antimony
Impure substances (mixtures): made up of element, compounds or both; combination of 2 or
more substances that aren’t chemically combined.
Properties of mixtures:
• No Chemical Changes in a Mixture No chemical changes happen when a mixture is made.
So, each substance has the same chemical makeup it had before the mixture was formed.
• Making a mixture is a physical change
•Separating Mixtures Through Physical Methods Mixtures can be separated by using
physical changes. Physical changes do not change the identities of the substances.
•Some methods could be distillation, evaporation, filtration, dissolve, use of magnets,
centrifuging,and chromatography
• The Ratio of Components in a Mixture The components of a mixture do not need to be
mixed in a definite ratio.
• For example, granite is a mixture of different minerals. Different ratios of the minerals give
granite different colors, but the mixture is always called granite.
Mixtures
Made of elements,
compunds or both
No change in original properties of
the components
Compunds
made of elements
Heat or electricity not required for
Separating the components
Heat or electricity required for
Separating the components
Made using any ratio of the
components
Made using a fixed ratio of
Components
change in original properties of
the components
5. Describe the components of a solution and the relation between them (solute, solvent,
concentration).
Solution: is a mixture that appears to be a single substance.
Solute: the substance that is dissolved.
Solvent: is the substance in which the solute is dissolved.
Concentration: is the amount of solute in a solution. A solution con be concentrated or dilute ,
because of the amount of solute in a solution
Solubility: is the ability of a solute to dissolve in a solvent at a certain temperature. Depends on
the attractions of solute particles for one another and attractions of solvent particles for one
another.
Dissolving Gases in Liquids Gases become less soluble in liquids as the temperature is raised.
Dissolving Solids Faster in Liquids Three ways to make a solute dissolve faster are mixing the
solution, heating the solution, and crushing the solute into smaller particles.
Unsaturate solution: A solution that has not reached the limit of solute that will dissolve
Saturated solution: A solution in which no more solute can be dissolved
Supersaturated solution: A solution that has more than the limit of a solute that can be
dissolved.
6. Describe the components of a solution and the relation between them (solute, solvent,
concentration).
Separating Mixtures Through Physical Methods Mixtures can be separated by using physical
changes. Physical changes do not change the identities of the substances.
Filtering: Pour a mixture (solid and liquid), through a filter paper. Depends on the solubility.
Crystallization: Slow formation of a solid from a warm solution that is cooled. Depends on the
solubility.
Distillation: Boil off and condense the more volatile component in a liquid mixture. Depends on
volatility.
.
Decanting: Used to separate a liquid from an insoluble solid. The solid stays in the bottom.
Chromatography: Involves the separation of different dissolved substances as they travel
through a material
Centrifugation: Involves the use of the centrifugal force. More dense components migrate
away. Solid particles remain on the bottom.
Evaporation: Separation of a liquid and a soluble solid.
Magnetism: A magnetically susceptible material is extracted from a mixture using a magnetic
force.
7. Use math skills to determine the ratio of various compounds.
Ratio of components:
Steps: divide the least number into the greatest number
Ex 18gH2O → 2g H2 + 16g O2
_ 2gH2__ = _1_
16g O2
8
Mass ratio: 1:8 if the ratio is different, is a different compound
Amount of atoms in the molecule : H3PO4 = 3+1+4 = 8
Amount of molecules: 3 molecules of CO how many molecules of O2 does it contain? = 3·2=
6 molecules
8. Explain how changes in matter are related to changes in energy.
Change of state: is the change of a substance from one physical form to another.
 The particles of a substance move differently depending on the state of the substance.
 The particles also have different amounts of energy when the substance is in different
states
When most substances lose or gain energy, one of two things happens to the substance: its
temperature changes or its state changes.
But the temperature of a substance does not change until a change of state is complete.
9. Become familiar with the following terms: energy, temperature, endothermic change,
exothermic change, condensation, sublimation, evaporation, melting, freezing, boiling.
Energy: power which may be translated into motion.
Temperature: A measure of intensity of heat.
Endothermic change: energy is gained by the substances as it changes state. Absorption of
heat.
Exothermic change: energy is removed from the substance as it changes state. Give off heat.
Condensation: the change of phase from gas to liquid , energy must be removed for
condensation to occur. Removing energy slows the movement of gas particles which allows
them to clump together.
Condensation point: is the temperature at which the gas becomes a liquid.
Sublimation: is the change of sate from solid to gas, For sublimation to occur, the attractions
between the particles must be completely overcome. So, the substance must gain energy during
sublimation.
Evaporation: the change of state from a liquid to a gas. Evaporation can occur at the surface
of a liquid that is below its boiling point.
It is a cooling process because in the process the particles with more kinetic energy are the
ones that leave the liquid first, and they are taking the energy away.
Melting: the change of state from a solid to a liquid. For a solid to melt, particles must
overcome their attractions to each other. We have to add energy
Melting point: is the temperature at which a solid changes to a liquid
Freezing: the change of state form liquid to a solid. When a liquid is at its freezing point,
removing energy will cause the particles to begin locking into place.
Freezing point: is the temperature at which a liquid changes to a solid
Boiling: is the change of a liquid to a gas throughout the liquid.
Boiling point: is the temperature at which a liquid boils.
10. Memorize the different elements and their symbols in English and Spanish.