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10 Neutral Atom

A neutral atom has no electric charge. Atoms are the building blocks of matter. Think of it as the stuff of which everything in the Universe is made. The center of an atom, called the nucleus, holds both protons, which are positively charged particles, and neutrons, which are particles with no charge. Electrons are negatively charged particles that spin around the nucleus at different distances called energy levels.

A neutral atom has an equal number of protons and electrons; thus, it has an overall net charge of zero. Much like the addition of +1 and −1 equals 0, the sum of one positive charge from one proton and one negative charge from one electron also equals zero.

The Bohr model of an atom looks much like a model of planets orbiting the Sun at different distances. Comparatively, in the Bohr model, negatively charged electrons orbit a positively charged nucleus in different energy levels. The Bohr model of an atom can be demonstrated with a paper model.

See for Yourself

Materials

 blank paper

 pencil

 scissors

 tape

What to Do

1 Fold the paper in half three times, once from top to bottom, and then from side to side, and last fold along a diagonal line so that the top folded edge meets the side fold as shown in Figure 1.FIG 1

2 Draw five curved lines on the top layer of the folded paper.

3 Cut along each of the five curved lines. Keep the three indicated sections as shown in Figure 2.FIG 2

4 Unfold the three sections; write “6p+” and “6n” in the circle, which represents the six protons and six neutrons in the nucleus of the atom.

5 In the smaller ring, draw two electrons (e−) on opposite sides, and in the largest ring, draw four electrons (e−) randomly spaced and as far apart as possible.

6 Connect the three parts by taping the string to each as shown in Figure 3. Secure the end of the string to a surface so that the atom model can hang freely.

FIG 3

What Happened?

This Bohr model is of the element carbon (C). The carbon atom model is neutral because it has six positively charged protons (p⁺) in its nucleus and six negatively charged electrons (e⁻) in the rings, which represent energy levels. In the Bohr model, atoms may hold up to two electrons in the first ring and up to eight electrons in the second ring. Since there are only a total of six electrons in a neutral atom of carbon, two electrons are in the first energy level and the remaining four electrons spread out in the second energy level, which is the outer ring. The electrons in the outer energy level of an atom are called valence electrons. The atom model of carbon has an overall charge of zero; thus, it is a neutral atom.