What is photosynthesis?
The process plants use light to make glucose from water and carbon dioxide, releasing oxygen.
What is the word equation for photosynthesis?
Water plus carbon dioxide produces glucose plus oxygen.
What pigment captures sunlight energy for photosynthesis?
Chlorophyll.
What happens when a glowing splint is placed in gas from photosynthesis?
The splint relights if the gas contains much oxygen.
How does increasing light intensity affect photosynthesis rate?
It increases the rate of photosynthesis.
Why does a water plant produce more bubbles when the lamp is closer?
Because higher light intensity increases photosynthesis rate.
What percentage of air is oxygen supplied largely by photosynthesis?
About 20%.
What are chloroplasts in plant cells?
Structures containing chlorophyll where photosynthesis occurs.
Which leaf layer contains cells that do most photosynthesis?
The palisade layer.
What is the main function of stomata in leaves?
Allow carbon dioxide entry and gas diffusion.
What color change indicates starch presence in a leaf test?
Starch turns blue-black with iodine solution.
Why is magnesium important for plants?
It is needed to make chlorophyll.
What symptom shows magnesium deficiency in plants?
Yellow leaves and reduced photosynthesis.
What does nitrate provide for plants?
Nitrogen to convert carbohydrates into proteins and make chlorophyll.
What symptoms indicate nitrate deficiency in plants?
Dying leaves and small plants.
What is the carbon cycle?
The movement of carbon atoms between air, organisms, decomposers, and fossil fuels.
What is the word equation for respiration?
Glucose plus oxygen produces carbon dioxide and water.
How does carbon move from air to plants in ecosystems?
Photosynthesis transfers carbon from air to plants.
How does carbon return to the air in ecosystems?
Respiration returns carbon dioxide to the air.
How are fossil fuels formed from dead organisms?
Pressure and heat change buried remains into fossil fuels in oxygen-poor places.
What happens to carbon during combustion of fossil fuels?
Carbon combines with oxygen to form carbon dioxide.
What distinguishes fossil fuels from fossils?
Fossil fuels are carbon fuels from ancient organisms; fossils are their remains turned to rock.
What is a greenhouse gas?
A gas that traps heat energy in the atmosphere and keeps Earth warm.
What releases carbon stored for millions of years as carbon dioxide?
Extracting and burning fossil fuels.
When did an asteroid collide with Earth causing mass extinction?
Around 67 million years ago.
What percentage of species became extinct due to the asteroid collision?
Up to 75% of species alive at the time.
How does increasing carbon dioxide concentration affect Earth's climate?
It traps more heat, raising temperature and causing extreme weather.
Why does sea level rise with global warming?
Because warmer water expands and melting ice adds water to oceans.
At what rate has sea level been rising recently?
About 3 mm per year.
How many people are at risk from sea-level flooding by century's end?
More than 600 million people.
What does the atomic number represent in an atom?
The number of protons in the atom.
What is the mass number of an atom?
The total number of protons and neutrons in the atom.
Why does an atom have no overall charge?
Because it has equal numbers of protons and electrons, and neutrons have no charge.
How many protons, electrons, and neutrons are in a lithium atom with atomic number 3 and mass number 7?
3 protons, 3 electrons, and 4 neutrons.
How many electrons can the first, second, and third shells hold?
First shell holds 2, second and third shells hold up to 8 electrons each.
How many electrons are in the outermost shell of Group 1, Group 7, and Group 8 elements?
Group 1 has 1, Group 7 has 7, and Group 8 has full outer shells.
What happens to atomic size and melting point down Group 1?
Atomic size increases and melting point decreases down the group.
What are the melting points of lithium, sodium, and potassium?
Lithium melts at 180 °C, sodium at 98 °C, and potassium at 63 °C.
What is an ion?
An atom or group of atoms with an electrical charge from gaining or losing electrons.
Why do atoms gain or lose electrons when reacting?
To achieve a full outermost electron shell for stability.
How do metals like sodium form ions?
By losing electrons to form positive ions.
How do non-metals like chlorine form ions?
By gaining electrons to form negative ions.
How does sodium chloride form?
Sodium loses one electron to Na⁺ and chlorine gains one to Cl⁻, forming NaCl by ionic bonding.
How does magnesium oxide form ions?
Magnesium loses two electrons to Mg²⁺ and oxygen gains two to O²⁻, producing MgO.
Why is potassium more reactive than lithium and sodium?
Its outer electron is furthest from the nucleus and lost most easily.
What is an ionic bond?
The electrostatic attraction between oppositely charged ions.
How does magnesium form magnesium oxide?
Magnesium loses two electrons to become Mg²⁺ and oxygen gains two electrons to become O²⁻.
What causes the attraction in magnesium oxide?
Oppositely charged ions attract each other.
What is a covalent bond?
A chemical bond formed when atoms share electrons.
Why does hydrogen chloride have the formula HCl?
Hydrogen and chlorine share one pair of electrons.
Why does ammonia have the formula NH₃?
Three hydrogen atoms share three pairs of electrons with one nitrogen atom.
What is a lattice in an ionic compound?
A giant regular structure of ions held by electrostatic forces.
How many Cl⁻ ions surround each Na⁺ ion in sodium chloride?
Six Cl⁻ ions surround each Na⁺ ion.
Why do ionic substances have high melting and boiling points?
Because strong electrostatic forces hold their ions together.
Why do simple covalent substances have low melting and boiling points?
Because weak intermolecular forces act between their molecules.
Why is diamond very hard?
Because each carbon atom forms four strong covalent bonds in a rigid 3D structure.
Why is graphite soft?
Because weak interlayer bonds allow layers to slide over one another.
Why do ionic compounds conduct electricity when melted or dissolved?
Because their charged ions are free to move.
Do simple covalent molecules conduct electricity?
No, simple covalent molecules do not conduct electricity.
In which year did Johann Dobereiner propose the law of triads?
1817
What pattern did John Newlands observe arranging elements by atomic mass?
Every eighth element had similar properties.
How did Dmitri Mendeleev modify Newlands's arrangement of elements?
He left gaps to group elements with similar properties together.
What did Mendeleev predict about undiscovered elements in his periodic table?
Their properties would fill the gaps and match his predictions.
What is the definition of density?
Mass per unit volume of a substance.
What is the formula to calculate density?
How is the volume of an irregular object measured?
By the increase in water volume when placed in a measuring cylinder.
What is absolute zero temperature in Celsius?
−273 °C
What does the law of conservation of energy state?
Energy cannot be created or destroyed, only changed or transferred.
What is a system in energy studies?
Something chosen to be studied, especially for energy changes.
How much light energy is produced from 100 J electrical energy in a lamp?
10 J of light energy is produced.
What is the total energy output when 100 J electrical energy is supplied to a lamp?
The total output remains 100 J.
How does dissipated energy differ from destroyed energy?
Dissipated energy spreads and becomes less useful; destroyed energy would no longer exist.
Can energy be destroyed according to the law of conservation?
Energy is dissipated but never destroyed.
In which direction does thermal energy always transfer?
From a hotter place to a colder place.
What happens to thermal energy when it moves from a hot object to a colder place?
The thermal energy is said to have dissipated.
What is conduction in thermal energy transfer?
Thermal energy transfer through vibrating particles pushing neighboring particles.
What causes convection currents in fluids?
Heated fluid expands, becomes less dense, rises, and colder fluid sinks.
What is the formula for density?
Density equals mass divided by volume.
How does increasing volume affect density if mass is constant?
Increasing volume decreases density.
What is radiation in thermal energy transfer?
Thermal energy transfer by invisible waves without particles.
Which surfaces are best at emitting and absorbing thermal radiation?
Dull, black surfaces with large surface area.
Which surfaces are worst at emitting and absorbing thermal radiation?
Shiny, white or silver surfaces with small surface area.
How does a vacuum flask reduce thermal energy transfer?
Its vacuum stops conduction and its silver surface reflects radiation.
What is evaporation in terms of state change?
Evaporation is the change from liquid to gas by high-energy particles escaping the surface.
What happens to the highest-energy particles during evaporation?
They leave the liquid surface during evaporation.
How does evaporation affect the temperature of the remaining liquid?
It lowers the liquid's temperature by reducing average particle energy.
Why does sweat cool the skin?
Because thermal energy from the skin evaporates sweat, removing heat.
What happens to body temperature in very humid conditions regarding sweat?
Body temperature can increase because sweat evaporates less effectively.
Why does sweat evaporate less effectively in humid conditions?
Because high humidity reduces the evaporative cooling effect.
How does particle force strength affect evaporation rate and sensation?
Weaker particle forces cause faster evaporation and a colder feeling.
What distinguishes evaporation speed between liquids at the same temperature?
Liquids with weaker intermolecular forces evaporate faster.
Test your knowledge with 66 questions on Chemical Bonding and Material Properties.
1. What does photosynthesis produce from water and carbon dioxide using light energy?
2. Which word equation correctly represents photosynthesis?
Review the complete course in the study sheet for Chemical Bonding and Material Properties.
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