When is the atomic number NOT equal to the number of electrons?

Explanation:

where there are negative or positive ions

Explanation:

Protons

Each element has an atomic number. The atomic numbers are listed along with the names and symbols of the elements on the inside cover of the text. The atomic number equals the charge on the nucleus. It therefore also equals the number of protons in the nucleus and also equals numerically the number of electrons in the neutral atom. The atomic number has the symbol Z.

Different elements have different atomic numbers; therefore, atoms of different elements contain different numbers of protons (and electrons). Oxygen has the atomic number 8; its atoms contain 8 protons and 8 electrons. Uranium has the atomic number 92; its atoms contain 92 protons and 92 electrons.

The relationship between atomic number and the number of protons or electrons can be stated as follows:

Atomic number= number of protons per atom= number of electrons per neutral atom

B. Mass Number Equals Protons plus Neutrons

Each atom also has a mass number, denoted by the symbol A. The mass number of an atom is equal to the number of protons plus the number of neutrons that it contains. In other words, the number of neutrons in any atom is its mass number minus its atomic number.

Number of neutrons = mass number - atomic number

or

Mass number = number of protons + number of neutrons

The atomic number and the mass number of an atom of an element can be shown by writing, in front of the symbol of the element, the mass number as a superscript and the atomic number as a subscript:

mass number

atomic numberSymbol of elementorA

ZX

For example, an atom of gold (symbol Au), with an atomic number 79 and mass number of 196 is denoted as:

196

79Au

C. Isotopes

Although all atoms of a given element must have the same atomic number, they need not all have the same mass number. For example, some atoms of carbon (atomic number 6) have a mass number of 12, others have a mass number of 13, and still others have a mass number of 14. These different kinds of the same element are called isotopes. Isotopes are atoms that have the same atomic number (and are therefore of the same element) but different mass numbers. The composition of atoms of the naturally occurring isotopes of carbon are shown in Table 4.2.

TABLE 4.2 The naturally occurring isotopes of 12

6C66613

6C66714

6C668

The various isotopes of an element can be designated by using superscripts and subscripts to show the mass number and the atomic number. They can also be identified by the name of the element with the mass number of the particular isotope. For example, as an alternative to

12

6C,13

6C,and14

6C

we can write carbon-12, carbon-13, and carbon-14.

About 350 isotopes occur naturally on Earth, and another 1500 have been produced artificially. The isotopes of a given element are by no means equally abundant. For example, 98.89% of all carbon occurring in nature is carbon-12, 1.11% is carbon-13, and only a trace is carbon-14. Some elements have only one naturally occurring isotope. Table 4.3 lists the naturally occurring isotopes of several common elements, along with their relative abundance.

TABLE 4.3 Relative abundance of naturally occurring isotopes of several elementsIsotopeAbundance (%)hydrogen-199.985hydrogen-20.015hydrogen-3tracecarbon-1298.89carbon-131.11carbon-14tracenitrogen-1499.63nitrogen-150.37 oxygen-1699.76oxygen-170.037oxygen-180.204IsotopeAbundance (%)silicon-2892.21silicon-294.70silicon-303.09chlorine-3575.53chlorine-3724.47phosphorus-31100iron-545.82iron-5696.66iron-572.19iron-580.33 aluminum-27100

what does the table look like

i'm wiling to try and you : )