Electrons, Nucleus, and Atomic Structure Help (page 2)

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By — McGraw-Hill Professional
Updated on Aug 28, 2011


A proton has a positive charge and roughly 1800 times greater mass than an electron.

A proton is a smaller bit of positively charged matter or sub-atomic particle within the nucleus.

The atomic number (Z) of an element is taken from the number of protons in the nucleus of an atom. A pure element is one that is made up of particles that all have the same atomic number.


To obtain the atomic number of an element, you must identify the number of protons in the nucleus.

What is the atomic number (Z) of (a) boron, (b) gold, (c) zinc, (d) iridium, and (e) bismuth? Did you get (a) 5, (b) 79, (c) 30, (d) 77, and (e) 83?


The nucleus of an atom contains sub-atomic particles called nucleons. Nucleons are divided into two kinds of particles, neutrons and protons . Protons make up the dense nucleus core, but when chemists made calculations based on atomic weights of atoms, the numbers didn’t add up. They knew there must be something they were missing. This is when neutrons were discovered. Neutrons are nuclear particles that have no charge and are located inside the crowded nucleus with positively charged protons.

Neutrons are sub-atomic particles with a similar mass to their partner proton in the nucleus but with no electrical (+ or –) charge.

Table 5.1 shows common characteristics of electrons, protons, and neutrons.

Table 5.1 Common characteristics of electrons, protons, and neutrons indicate their special nature.

Atoms, Elements, and Compounds The Nucleus Neutron

Atomic Structure

Though Thomson, Rutherford, Meyer and Mendeleyev didn’t quite understand what caused many of the reactions they observed, they recorded the patterns they saw among the elements. They noted that elemental properties seemed to reflect atomic weight and atomic number, but weren’t really sure why. Modern chemistry has discovered the answers to these puzzles.

Figure 5.3 illustrates a beryllium atom with its energy levels. The atom is composed of 4 protons and 5 neutrons in the nucleus, and 4 electrons arranged in 2 shells (or orbital layers) outside the nucleus. The first shell contains 2 electrons and the second shell contains 2 electrons.

Atoms, Elements, and Compounds Atomic Structure

Fig. 5.3. Beryllium atom with its energy levels.

Through detailed experiments, scientists discovered that the way an element behaves is largely due to the number of electrons in its outer orbital shells. For example, elements with one electron in the outer shell behave alike; those with two electrons behave alike, and so on. This knowledge allowed early chemists to place similar elements in the same Periodic Table groups according to their outermost or valence electrons.


Practice problems for these concepts can be found at - Atoms, Elements, and Compounds Practice Test


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