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Grade 8 Natural Sciences – Matter and Material Flashcards

Explore key Grade 8 concepts on matter, states, density, diffusion, and the periodic table, presented in clear, concise language for effective learning.

17 cards~6 min
Grade 8 Natural Sciences – Matter and Material Flashcards — Qwi
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1What are the horizontal rows on the Periodic Table called?
Answer

Periods

Rows are called periods because each row represents a period of elements with increasing atomic number.
2What must an atom have to be neutral if it has 12 protons?
Answer

12 electrons around the nucleus

A neutral atom has equal numbers of protons and electrons.
3Which property distinguishes a solid from liquids and gases?
Answer

It has a defined shape.

Solids maintain a fixed shape because their particles are tightly packed.
4What state change does melting represent?
Answer

Solid to liquid.

Melting converts a solid into a liquid by adding heat.
5How does the density of water as a solid compare to its liquid form?
Answer

Less dense as a solid than a liquid.

Ice floats because its density is lower than liquid water.
6A sub‑atomic particle with a positive charge is called {{proton}}.
Answer

proton

7What is diffusion?
Answer

Spontaneous spreading of particles from high to low concentration.

Diffusion occurs due to random motion of particles moving down a concentration gradient.
8How does diffusion in liquids compare to diffusion in gases?
Answer

Liquids: slower | Gases: faster

Because gas particles are farther apart and have weaker intermolecular forces, they spread more quickly.
9Diffusion can occur in solids.
Answer

False

In solids, particles are fixed in place, preventing diffusion.
10Define density.
Answer

Mass per unit volume.

Density quantifies how much mass is contained in a given volume.
11Order the substances water, sand, and ice from highest to lowest density.
Answer

Sand > Water > Ice

Sand is most dense, water less, ice least due to its crystal structure.
12Why can a ship float on water?
Answer

Because the ship’s average density is less than water’s.

Buoyant force equals weight of displaced water; if density is lower, it stays afloat.
13What causes the lid to pop off when more air is pumped into a sealed tin?
Answer

Increasing internal pressure.

Adding air raises pressure until it exceeds the lid’s holding force, causing it to pop off.
14The symbol for hydrogen is {{H}}.
Answer

H

15Protons and neutrons determine the mass of an atom.
Answer

True

Mass is mainly from protons and neutrons; electrons contribute negligible mass.
16Difference between an element, a compound, and a mixture?
Answer

Element: single type of atom | Compound: chemically bonded atoms | Mixture: physical combination of substances

Elements cannot be broken down by chemical means, compounds have fixed ratios, mixtures retain individual components.
17What is electrolysis?
Answer

The process of using electric current to cause a chemical change.

Electrolysis splits compounds into their constituent elements at electrodes.

Understanding Matter and Its Properties

Matter is anything that occupies space and has mass. In Grade 8 natural sciences, students learn to describe matter using measurable properties such as shape, volume, mass, and density. These properties help differentiate solids, liquids, and gases and explain everyday phenomena.

States of Matter

Three common states of matter are solid, liquid, and gas. Each state has distinct characteristics:

  • Solid: has a defined shape because its particles are tightly packed in a fixed arrangement.
  • Liquid: takes the shape of its container while maintaining a constant volume; particles are less tightly bound than in solids.
  • Gas: has neither a fixed shape nor a fixed volume; particles are far apart and move freely.

When heat is added to a solid, it undergoes melting, a state change from solid to liquid. Conversely, removing heat can cause freezing, turning a liquid into a solid.

Density and Buoyancy

Density is defined as mass per unit volume (density = mass ÷ volume). It determines whether an object sinks or floats in a fluid. For example, ice is less dense than liquid water, so it floats. Sand, water, and ice ordered from highest to lowest density are:

  1. Sand
  2. Water
  3. Ice

A ship floats because its average density is lower than that of water, allowing the buoyant force (equal to the weight of displaced water) to keep it afloat.

Pressure in Closed Systems

When air is pumped into a sealed container, the internal pressure increases. If the pressure exceeds the force holding the lid, the lid will pop off. This illustrates the relationship between pressure, volume, and the amount of gas in a closed system.

The Periodic Table

The periodic table organizes all known elements. Horizontal rows are called periods. Each period represents a sequence of elements with increasing atomic number, reflecting a gradual change in properties.

Elements are identified by symbols; for example, hydrogen is represented by H. An atom is neutral when it has an equal number of protons and electrons. Therefore, an atom with 12 protons must also have 12 electrons to remain neutral.

Atomic Structure and Mass

Protons and neutrons, located in the nucleus, determine the mass of an atom. Electrons contribute negligible mass. A positively charged sub‑atomic particle is called a proton.

Diffusion and Molecular Motion

Diffusion is the spontaneous spreading of particles from regions of high concentration to regions of low concentration. It occurs because particles move randomly, seeking equilibrium.

Diffusion rates differ among states of matter:

  • In gases, diffusion is rapid because particles are far apart and experience weak intermolecular forces.
  • In liquids, diffusion is slower due to closer particle spacing and stronger intermolecular forces.
  • In solids, diffusion essentially does not occur because particles are fixed in place.

Classification of Substances

Substances can be categorized as elements, compounds, or mixtures:

Category Definition
Element Consists of a single type of atom; cannot be broken down by chemical means.
Compound Atoms chemically bonded in fixed ratios; can be broken down into elements.
Mixture Physical combination of two or more substances; components retain their individual properties.

Electrolysis

Electrolysis is the process of using electric current to drive a chemical change, typically splitting a compound into its constituent elements at the electrodes.

Key Takeaways

  • Solids have a defined shape; liquids adopt the shape of their container; gases expand to fill any space.
  • Density (mass/volume) explains why ice floats and why ships stay afloat.
  • Periods are the horizontal rows of the periodic table, each representing a sequential increase in atomic number.
  • Neutral atoms have equal numbers of protons and electrons.
  • Diffusion occurs spontaneously, faster in gases than in liquids, and is negligible in solids.
  • Elements, compounds, and mixtures differ in composition and bonding.
  • Electrolysis uses electricity to cause chemical reactions, separating compounds into elements.