Pure or Mix?
What is a substance made of only one type of particle called?
A PURE SUBSTANCE
How many protons, neutrons, and electrons does an atom of HELIUM (He) have?
A helium atom has 2 protons, 2 neutrons, and 2 electrons.
An ice cube is left sitting out on a laboratory bench. Over ten minutes, it turns into a puddle of clear liquid water.
A PHYSICAL change has occurred.
What do elements in the same group (column) of the periodic table generally have in common?
They have the same number of valence electrons and similar chemical properties.
Which state of matter has a DEFINITE SHAPE and DEFINITE VOLUME?
Is gold (Au) an element, compound, or mixture?
How many protons, neutrons, and electrons does an atom of SODIUM (Na) have?
A sodium (Na) atom has 11 protons, 11 electrons, and 12 neutrons.
An iron padlock is left outside in the damp rain for three weeks. It turns a flaky, brittle, reddish-brown color.
A CHEMICAL change has occurred.
As you move from left to right across a period, what happens to the number of protons?
It increases.
In which state are particles FAR APART and able to move FREELY?
A GAS
A particle diagram shows identical groups of one red particle bonded to two blue particles throughout the sample. Is this a pure substance or mixture? Explain.
Pure substance/compound, because every particle is the same type of molecule and the atoms in the molecule are bonded together chemically.
How many protons, neutrons, and electrons does an atom of ALUMINUM (Al) have?
An atom of aluminum (Al) has 13 protons, 13 electrons, and 14 neutrons.
A spoonful of white table sugar is stirred into a glass of warm water until the crystals are completely out of sight.
A PHYSICAL change has occurred.
An element is located in Group 17. How many valence electrons would you expect it to have?
7 valence electrons
What happens to the motion of particles when THERMAL ENERGY IS ADDED?
Particles MOVE FASTER.
A sample contains individual red atoms, individual blue atoms, and groups of red-and-blue atoms. Is this a pure substance or a mixture? Explain how the particle diagram shows this.
Mixture, because there are multiple types of particles present.
For a FLUORINE (F) atom, how many electrons are on each energy level?
1-? 2-? 3-?
1-2
2-7
3-0
A strip of dull silver magnesium metal is held over a Bunsen burner. It ignites into a blinding white light, leaving a white ash behind.
A CHEMICAL change has occurred.
An unknown element has 2 valence electrons and is in Period 4. Where would you find it on the periodic table?
Group 2, Period 4 — CALCIUM (Ca)
A substance changes from a LIQUID to a GAS. What happens to its particles as THERMAL ENERGY was ADDED?
The particles gain thermal energy, MOVE FASTER, and SPREAD FARTHER APART.
Two samples look exactly the same to the naked eye. Sample A contains only one type of particle. Sample B contains two different types of particles that are evenly distributed. Classify each sample and explain how you could tell them apart using a particle model.
A = pure substance. B = homogeneous mixture. A particle model would show one particle type in A and two particle types evenly (uniformly) distributed in B.
Draw a model of an atom of CHLORINE (Cl).
Teacher's Choice!
You bend a plastic glow stick until a tiny glass vial cracks inside. Suddenly, the two mixed liquids begin emitting a bright neon green glow.
A CHEMICAL change has occurred.
Which element is larger: LITHIUM (Li) or FLUORINE (F)?
Lithium (Li) is larger than fluorine (F).
A student says, “When ice melts, the particles themselves become liquid particles.” Is the student correct? Explain what actually happens at the particle level.
No. The particles are still the same substance. They gain thermal energy, move more freely, and change from the organized arrangement of a solid to the less restricted movement of a liquid. The particles themselves do not change.