science - Mid term

What are qualitative observations?

 Descriptions using your five senses (sight, sound, smell, touch, taste) without numbers. Examples: "red color," "fizzing sound," "smooth texture"

What are quantitative observations?

 Measurements with numbers and units. Examples: "5.2 cm long," "15°C temperature," "3 bubbles formed"

What is an inference?

A logical conclusion based on observations. Example: "The grass is wet so I can infer it rained" (NOT an if-then statement and NOT a prediction)

What is a prediction?

An educated guess about future events based on past patterns. Made BEFORE experiments start.

What is a hypothesis?

An educated guess written in "If...then...because" format predicting experiment results

What is the independent/manipulated variable?

 The variable that YOU change or control in an experiment

 What is the dependent/responding variable?

The variable you measure or observe; it responds to changes in the independent variable

What are controlled variables?

All the variables kept the same in an experiment so only the independent variable affects results

What does a ruler measure?

Length in centimeters (cm) or millimeters (mm)

What does a balance measure?

 Mass in grams (g)

What does a graduated cylinder measure?

 Volume of liquids in milliliters (mL). Read at eye level at the bottom of the meniscus.

How do you calculate volume of a regular object?

Length × Width × Height (L × W × H)

How do you find volume of an irregular object?

Water displacement method: Final water level - Initial water level = Object volume

 What are physical properties?

Characteristics you can observe WITHOUT changing the substance's chemical identity. Examples: color, density, melting point, hardness

What are chemical properties?

Properties that describe how a substance reacts with other substances. Examples: flammability, reactivity with acids, ability to rust

What are physical changes?

Changes in form where the chemical identity stays the same. Examples: melting, cutting, dissolving sugar

What are chemical changes?

Changes that form new substances with different properties. Examples: burning, rusting, digesting

What is mass?

 The amount of matter in an object, measured in grams. Stays the same everywhere in the universe.

 What is weight?

The force of gravity pulling on mass. Changes depending on gravitational pull (less on moon).

What is density and its formula?

How much mass is packed into a given volume. Formula: Density = Mass ÷ Volume (D = m/V). Units: g/mL or g/cm³

How does density affect floating and sinking?

Less dense materials float on more dense materials. Example: Oil floats on water, ice floats on liquid water.

What is a homogeneous mixture?

 A mixture with uniform composition throughout; you cannot see individual components. Examples: salt water, air

What is a heterogeneous mixture?

A mixture where you can see different parts; non-uniform composition. Examples: oil and water, trail mix

Name four methods to separate mixtures

Filtration (particle size), distillation (boiling points), chromatography (movement through materials), magnetism (magnetic properties)

How are particles arranged in solids?

Tightly packed together, vibrate in place

How are particles arranged in liquids?

 Close together but can slide past each other

How are particles arranged in gases?

Spread far apart, move freely and rapidly

What is melting?

Phase change from solid to liquid (endothermic - absorbs heat)

What is freezing?

Phase change from liquid to solid (exothermic - releases heat)

What is vaporization?

Phase change from liquid to gas; includes boiling and evaporation (endothermic - absorbs heat)

What is condensation?

Phase change from gas to liquid (exothermic - releases heat)

What is sublimation?

Phase change from solid directly to gas (like dry ice) (endothermic - absorbs heat)

What is deposition?

 Phase change from gas directly to solid (exothermic - releases heat)

What happens to temperature during a phase change?

Temperature stays CONSTANT. Energy goes into breaking or forming intermolecular forces, not changing temperature.

 What are endothermic phase changes?

Phase changes that ABSORB heat: melting, vaporization, sublimation (particles speed up)

What are exothermic phase changes?

Phase changes that RELEASE heat: freezing, condensation, deposition

What is boiling point?

The specific temperature at which a liquid changes to gas throughout the entire substance (212F - 100C)

What are protons?

Positively charged particles in the nucleus that determine what element an atom is (Top left number same as atomic number and electrons if element is not an ion)

What are neutrons

Particles with no charge in the nucleus. (Neutrons= Rounded atomic mass- atomic number)

 What are electrons?

Negatively charged particles that orbit the nucleus in shells (Same number as proton and atomic number only if the element is not an ion)

What is atomic number?

The number of protons in an atom; determines the element's identity

What is atomic mass?

The number of protons plus neutrons

 In a neutral atom, how do protons and electrons compare?

The number of protons equals the number of electrons

What are valence electrons?

Electrons in the outermost shell that determine how atoms bond (Same as their group number but -10 if group is 13-18)

 Which element has no neutrons?

Hydrogen is the only element with no neutrons

 What are periods on the periodic table?

Horizontal rows; elements in the same period have the same number of electron shells

What are groups on the periodic table?

Vertical columns; elements in the same group have the same number of valence electrons and similar properties

How are elements arranged on the periodic table?

By increasing atomic number (number of protons)

What are metals?

Elements on the left side of the periodic table; shiny, conduct electricity, malleable

What are nonmetals?

 Elements on the right side of the periodic table; dull, don't conduct electricity

What are metalloids?

Elements along the zigzag line; have properties between metals and nonmetals

What are noble gases?

Group 18 elements with full outer electron shells; very unreactive

What are ionic bonds?

Bonds formed when electrons are transferred from metal atoms to nonmetal atoms

What are covalent bonds?

Bonds formed when nonmetal atoms share electrons

What do atoms want to achieve when bonding?

 Full outer electron shells (usually 8 electrons)

If 5g of substance A reacts with 10g of substance B, what is the total mass of products? B

 15g (5g + 10g = 15g total mass is conserved)

What happens to atoms during chemical reactions?

Atoms rearrange to form new substances, but the total number and type of atoms stays the same

What does H₂O tell you?

 Water molecule with 2 hydrogen atoms and 1 oxygen atom

 What does the chemical symbol Na represent?

Sodium (from Latin "natrium")

What does the chemical symbol Cl represent?

chlorine

What must be equal on both sides of a balanced chemical equation?

The number of each type of atom

What do flat horizontal lines mean on a phase change diagram?

Phase changes are happening; temperature stays constant while energy breaks/forms bonds

 What do sloped lines mean on a phase change diagram?

Temperature is changing within one phase; no phase change occurring