Which cube contains more atoms

Ask students: How can two objects, which are exactly the same size and shape, have a different mass? Help students understand that the difference in mass must have something to do with the atoms in each cube. There are three possible explanations about the copper and aluminum atoms in the cubes that could explain the difference in mass. Copper atoms might have more mass than aluminum atoms. Copper atoms might be smaller so more can fit in the same volume.

Copper and aluminum atoms might be arranged differently so more copper atoms fit in the same size cube. Give each student an activity sheet. Project an illustration and use the pictures of the copper and aluminum atoms to introduce the concept of density.

Show students the image Aluminum and Copper Atoms Point out that the copper atoms are slightly smaller than aluminum atoms. Show animations and demonstrate how to measure volume and mass of a cube. Show the animation Cube. Volume The cubes are 2. Show students that in order to calculate the volume, you multiply the length 2. Rounding this number to Record the volume of the cube in cubic centimeters cm 3. Mass Demonstrate how to use the balance that students will be using to measure the mass of the cube.

Record the mass of the cube in grams g. Density Show students how to calculate density by dividing the mass by the volume. Explore Have students calculate the density of eight different cubes and use the characteristic property of density to correctly identify them.

Question to investigate Can you use density to identify eight cubes made of different materials? Materials for the class Set of eight cubes of equal volume Calculator Teacher preparation Use a piece of masking tape and a permanent marker to mark the eight cubes with the letters A—H. Materials for each group Cubes marked A—H that you will share with other groups Balance that can measure in grams Calculator Procedure The volume of each cube is given in the chart.

It is Find the mass in grams of each cube using a scale or balance. Record this mass in the chart. Trade cubes with other groups until you have measured the mass of all eight cubes. Table 1. Approximate densities for various materials. Write the name of the material in your chart for cubes A—H. Explain Discuss how the mass, size, and arrangement of atoms and molecules affect the densities of metal, plastic, and wood Explain to students that each substance has its own density because of the atoms and molecules it is made from.

Metal Project the image Metal Most common metals like aluminum, copper, and iron are more dense than plastic or wood. The atoms that make up metals are generally heavier than the atoms in plastic and wood and they are packed closer together. The difference in density between different metals is usually bsed on the size and the mass of the atoms but the arrangement of the atoms in most metals is mostly the same.

Plastic Project the image Plastic Most plastics are less dense than metal but can have similar density to wood. Plastics are made from individual molecules bonded together into long chains called polymers. These polymer chains are arranged and packed together to make the plastic.

One common plastic, polyethylene, is made up of many individual molecules called ethylene which bonded together to make the long polymer chains. Like most plastics, the polymers in polyethylene are made of carbon and hydrogen atoms. The carbon and hydrogen atoms are very light, which helps give plastics their relatively low density.

Plastics can have different densities because different atoms can be attached to the carbon-hydrogen chains. The density of different plastics also depends on the closeness of packing of these polymer chains. Wood Project the image Wood Wood is made mostly from carbon, hydrogen, and oxygen atoms bonded together into a molecule called glucose.

These glucose molecules are bonded together to form long chains called cellulose. Many cellulose molecules stacked together give wood its structure and density. Ask students: The size, mass, and arrangement of atoms affect the density of a substance. How might these factors work together to cause a substance to have a high density?

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The volume of a unit cell of calcium is 0. Silver crystallizes in a cubic lattice. Its unit cell of contains 4 atom We can calculate the number of atoms in your head if we know the density and a constant called Avogadro's number. This is really just an estimate, but it's going to be a good one. The equation is fairly simple. The number of atoms of ANY substance in a volume is:. N is a constant called Avogadro's number and its equal to 6.

It can also be molecules per mole. In the above formula density times volume is just the mass. If you know how heavy something is or what its volume and density are you can easily do this. Lets start with a simple problem. A liter of water is cubic centimeters. Water is easy because each cubic centimeter has 1 gram of mass.