VALID Science 10 cheat sheet

Independent variable is the factor deliberately changed by the experimenter; dependent variable is the measured response; controlled variables are held constant.

A hypothesis must be testable and falsifiable; a prediction states the expected outcome if the hypothesis is true.

Control group receives no treatment or a placebo so the effect of the treatment can be isolated by comparison.

Repeat trials and larger sample sizes reduce the influence of random error and increase reliability of results.

Accuracy is closeness to the true value; precision is closeness of repeated measurements to each other.

A valid conclusion requires that only the independent variable differ between experimental and control groups.

Correlation between two variables does not establish causation; a confounding variable may explain both.

Report data in tables and graphs with units on axes; a line graph suits continuous data, a bar graph suits categories.

Atoms contain protons (positive, in nucleus), neutrons (neutral, in nucleus), and electrons (negative, in shells or orbitals).

Atomic number equals the number of protons and identifies the element; in a neutral atom it also equals electron count.

Mass number equals protons plus neutrons; isotopes of an element differ in neutron number only.

Electrons fill shells in order 2, 8, 8 for the first three shells; the outermost (valence) electrons govern reactivity.

Periodic table rows are periods (same number of electron shells); columns are groups (same number of valence electrons).

Group 1 alkali metals are highly reactive, losing one electron; Group 17 halogens gain one electron; Group 18 noble gases are stable and unreactive.

Metals lie left of the metalloid staircase, are conductive and malleable; nonmetals lie right; metalloids have intermediate properties.

Atomic radius decreases across a period and increases down a group; ionization energy generally increases across a period.

Law of conservation of mass: total mass of reactants equals total mass of products in a closed system.

Balancing equations changes coefficients only, never subscripts, so atom counts match on both sides.

Synthesis: A + B yields AB; decomposition: AB yields A + B; single replacement: A + BC yields AC + B; double replacement: AB + CD yields AD + CB.

Combustion of a hydrocarbon with oxygen produces carbon dioxide and water; complete combustion needs excess oxygen.

Signs of chemical change include gas production, precipitate formation, color change, and temperature change.

Exothermic reactions release energy to surroundings (temperature rises); endothermic reactions absorb energy (temperature falls).

Reaction rate increases with higher temperature, higher concentration, greater surface area, or addition of a catalyst.

In a closed system, mass measured before and after a reaction is unchanged even when a gas forms.

Ionic bonds form between metal and nonmetal by transfer of electrons; the resulting ions are held by electrostatic attraction.

Covalent bonds form between nonmetals by sharing electron pairs; molecules result.

Ionic compounds have high melting points and conduct electricity when molten or dissolved, not as solids.

Write ionic formulas by balancing charges: calcium ion 2+ with chloride 1- gives CaCl2.

Name ionic compounds as metal name plus nonmetal stem with -ide suffix; include Roman numerals for variable-charge metals such as iron(II).

Name binary covalent compounds with prefixes mono-, di-, tri-, tetra- and the -ide suffix, for example dinitrogen monoxide.

A subscript counts atoms in a formula; a coefficient counts formula units in an equation.

Water is polar and dissolves ionic and polar substances; nonpolar substances dissolve in nonpolar solvents.

Speed equals distance divided by time; velocity is speed with direction; acceleration is change in velocity divided by time.

Newton's first law: an object stays at rest or in uniform motion unless a net force acts on it.

Newton's second law: net force equals mass times acceleration (F = ma); acceleration is proportional to force and inversely proportional to mass.

Newton's third law: every action force has an equal and opposite reaction force on a different object.

Weight equals mass times gravitational field strength (about 9.8 N/kg on Earth); mass is constant, weight varies with gravity.

Kinetic energy equals one-half mass times velocity squared; gravitational potential energy equals mass times gravity times height.

Work equals force times distance moved along the force direction; power equals work divided by time.

Energy is conserved but transforms among forms; friction converts mechanical energy to thermal energy.

Current is the rate of charge flow, measured in amperes; voltage is energy per unit charge, measured in volts.

Ohm's law: voltage equals current times resistance (V = IR); resistance is measured in ohms.

In a series circuit, current is the same through all components and voltages add; total resistance is the sum.

In a parallel circuit, voltage is the same across branches and currents add; total resistance is less than the smallest branch.

Power equals voltage times current (P = VI); energy used equals power times time.

Conductors allow charge flow (metals); insulators resist it (rubber, glass); resistance rises with length and falls with cross-sectional area.

Ammeters are connected in series with a component; voltmeters are connected in parallel across it.

Static charge builds by transfer of electrons through friction; like charges repel, opposite charges attract.

Earth's layers from outside inward: crust, mantle, outer core (liquid), inner core (solid); the lithosphere includes crust and upper mantle.

Tectonic plates move on the asthenosphere; divergent boundaries create new crust, convergent boundaries destroy or uplift crust, transform boundaries slide past.

At convergent boundaries, subduction produces trenches, volcanic arcs, and earthquakes; continent-continent collision builds mountains.

Seafloor spreading at mid-ocean ridges produces new oceanic crust and records magnetic reversals in stripes.

Earthquakes occur where stress releases suddenly along faults; epicenter is the surface point above the focus.

The Richter or moment magnitude scale is logarithmic; each whole step is about 32 times more energy.

Weathering and erosion break and transport rock; deposition and compaction form sedimentary rock.

The rock cycle links igneous, sedimentary, and metamorphic rocks through melting, cooling, weathering, and heat and pressure.

Atmosphere layers from surface upward: troposphere (weather), stratosphere (ozone layer), mesosphere, thermosphere.

Air pressure decreases with altitude; wind flows from high pressure to low pressure areas.

Uneven solar heating causes convection; warm air rises and expands, cool air sinks and contracts.

Relative humidity is the amount of water vapor present compared with the maximum the air can hold at that temperature.

Clouds form when rising moist air cools to the dew point and water vapor condenses on condensation nuclei.

High-pressure systems bring clear, stable weather; low-pressure systems bring clouds and precipitation.

Climate is long-term average weather patterns; weather is short-term atmospheric conditions.

Greenhouse gases such as carbon dioxide and water vapor absorb and re-emit infrared radiation, warming the surface.

Cell theory: all living things are made of cells, cells are the basic unit of life, and new cells arise from existing cells.

Prokaryotic cells lack a nucleus and membrane-bound organelles; eukaryotic cells have both.

Mitochondria release energy through cellular respiration; chloroplasts perform photosynthesis; ribosomes build proteins.

Mitosis produces two genetically identical diploid cells for growth and repair; meiosis produces four genetically varied haploid gametes.

DNA is a double helix of nucleotides with bases adenine-thymine and guanine-cytosine; genes are DNA segments coding for traits.

Genotype is the allele combination; phenotype is the observable trait; dominant alleles mask recessive alleles in heterozygotes.

A Punnett square predicts offspring genotype ratios from parental alleles, for example a cross of two heterozygotes gives 1:2:1.

Sexual reproduction combines gametes and increases genetic variation; asexual reproduction produces clones.

Food chains show energy flow from producers to consumers; arrows point in the direction of energy transfer.

Only about 10 percent of energy passes to the next trophic level; the rest is lost as heat and waste, so food chains are short.

Decomposers break down dead matter and recycle nutrients back to producers.

A population is one species in an area; a community is all populations; an ecosystem includes the community and abiotic factors.

Carrying capacity is the maximum population an ecosystem can sustain; limiting factors include food, water, and space.

Predator-prey, competition, and mutualism are interactions that regulate population sizes.

Biodiversity increases ecosystem resilience; habitat loss and invasive species reduce it.

Sustainability means using resources at a rate that allows natural replacement; renewable resources can regenerate, nonrenewable cannot.