2.28. Atoms http://www.ck12.org
FIGURE 2.52
Model of a helium atom.Q:Lithium has three protons, four neutrons, and three electrons. Sketch a model of a lithium atom, similar to the
model 2.52 for helium.
A:Does your sketch resemble the model in theFigure2.53? The model has three protons (red) and four neutrons
(blue) in the nucleus, with three electrons (gray) moving around the nucleus. You can see an animated model of a
lithium atom at this URL: http://ippex.pppl.gov/interactive/matter/elements.html.
Q:All atoms of carbon have six protons. How many electrons do carbon atoms have?
A:Carbon atoms must have six electrons to “cancel out” the positive charges of the six protons. That’s because
atoms are always neutral in electric charge.
Summary
- Atoms are the building blocks of matter. They are the smallest particles of an element that still have the
element’s properties. - All atoms are very small, but atoms of different elements vary in size.
- Three main types of particles that make up all atoms are protons, neutrons, and electrons.
Vocabulary
- atom: Smallest particle of an element that still has the element’s properties.
Explore More
Examine the animated atomic models at the following URL, and then answer the questions below.
http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-animations.shtml