PS1-2: Intro Atoms and Molecules

Like all matter, atoms have mass and volume.

But atoms are extremely small. A water droplet, like the one hanging

from the tip of the leaf in this picture, contains more than a billion

trillion atoms!

Which of the following statements is true?

• Atoms don't have mass

• Atoms can be seen with the naked eye

• Atoms make up every substance around you

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Almost all of an atom's mass is found in its _________, located in the center of the atom. An atom's nucleus can contain two types of particles: protons and neutrons.

The nucleus of every atom contains one or more _______. Each proton has a positive electrical charge.

In many atoms, the nucleus also contains __________. A neutron has no electrical charge.

• outer shell; protons; electrons

• nucleus; electrons; protons

• outer shell; electrons; neutrons

• nucleus; protons; neutrons

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Protons and neutrons are found in the nucleus of an atom. Traveling around the nucleus are fast-moving particles called electrons. Each electron has a negative electrical charge. An electron is much smaller and lighter than a proton or a neutron.

Which of the following statements are true? Select all that apply.

• All of an atom's electrons are found outside the nucleus

• A proton is the same size as an electron

• An electron has a negative electric charge

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Because atoms are so hard to see, people use atomic models to represent the way protons, neutrons, and electrons are arranged in an atom.

The diagram below is an example of an atomic model. In this model, a positive electrical charge is shown with the plus symbol (+) and a negative electrical charge is shown with the minus symbol (–).

Use the words below to label each part of the model.

atom proton neutron electron

• 1 atom 2 proton 3 neutron 4 electron

• 1 neutron 2 electron 3 atom 4 proton

• 1 atom 2 proton 3 electron 4 neutron

• 1 electron 2 neutron 3 proton 4 atom

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Each model represents a different atom.

The two atoms represented above contain the same number of ___

• atoms

• electrons

• neutrons

• protons

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The number of protons in an atom is known as its atomic number. Atoms that share the same atomic number are classified as the same chemical element.

Above is a model representing an atom of the chemical element lithium.

Lithium's atomic number is 3 because it has 3 protons.

What other model could represent lithium?

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In addition to having a unique name and atomic number, every chemical element has a unique atomic symbol.

The atomic symbol for a chemical element is a short version of its name. The atomic symbol consists of one or two letters. The first letter is always capitalized.

Sometimes an atomic symbol represents the name of the chemical element in a different language. For example, the atomic symbol Ag is short for the Latin word argentum, which means silver.

The atomic symbol ________ represents the chemical element_______.

• nickel...Ni

• Ni...nickel

Both the chemical formula and the model tell you about the composition of water. But only the model gives you information about the arrangement of the atoms in a water molecule.

composition is __________ ; arrangement is _______

• the chemical elements that make up a substance; the order and shape in which the atoms are bound together in a substance

• the order and shape in which the atoms are bound together in a substance; the chemical elements that make up a substance

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The models below represent molecules of three different substances. Each substance has a different chemical formula.

Select the model that represents a molecule of the substance with the chemical formula ICl.

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Select the model that represents a molecule of the substance with the chemical formula NH3.

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