<< Chapter < Page Chapter >> Page >

Electrons fill orbitals in a consistent order: they first fill the orbitals closest to the nucleus, then they continue to fill orbitals of increasing energy further from the nucleus. If there are multiple orbitals of equal energy, they will be filled with one electron in each energy level before a second electron is added. The electrons of the outermost energy level determine the energetic stability of the atom and its tendency to form chemical bonds with other atoms to form molecules.

Under standard conditions, atoms fill the inner shells first, often resulting in a variable number of electrons in the outermost shell. The innermost shell has a maximum of two electrons but the next two electron shells can each have a maximum of eight electrons. This is known as the octet rule    , which states, with the exception of the innermost shell, that atoms are more stable energetically when they have eight electrons in their valence shell    , the outermost electron shell. Examples of some neutral atoms and their electron configurations are shown in [link] . Notice that in this [link] , helium has a complete outer electron shell, with two electrons filling its first and only shell. Similarly, neon has a complete outer 2n shell containing eight electrons. In contrast, chlorine and sodium have seven and one in their outer shells, respectively, but theoretically they would be more energetically stable if they followed the octet rule and had eight.

Art connection

Bohr diagrams of elements from groups 1, 14, 17 and 18, and periods 1, 2 and 3 are shown. Period 1, in which the 1n shell is filling, contains hydrogen and helium. Hydrogen, in group 1, has one valence electron. Helium, in group 18, has two valence electrons. The 1n shell holds a maximum of two electrons, so the shell is full and the electron configuration is stable. Period 2, in which the 2n shell is filling, contains lithium, carbon, fluorine, and neon. Lithium, in group 1, has 1 valence electron. Carbon, in group 14, has 4 valence electrons. Fluorine, in group 17, has 7 valence electrons. Neon, in group 18, has 8 valence electrons, a full octet. Period 3, in which the 3n shell is filling, contains sodium, silicon, chlorine, and argon. Sodium, in group 1, has 1 valence electron. Silicon, in group 14, has 4 valence electrons. Chlorine, in group 17, has 7 valence electrons. Argon, in group 18, has 8 valence electrons, a full octet.
Bohr diagrams indicate how many electrons fill each principal shell. Group 18 elements (helium, neon, and argon are shown) have a full outer, or valence, shell. A full valence shell is the most stable electron configuration. Elements in other groups have partially filled valence shells and gain or lose electrons to achieve a stable electron configuration.

An atom may give, take, or share electrons with another atom to achieve a full valence shell, the most stable electron configuration. Looking at this figure, how many electrons do elements in group 1 need to lose in order to achieve a stable electron configuration? How many electrons do elements in groups 14 and 17 need to gain to achieve a stable configuration?

Understanding that the organization of the periodic table is based on the total number of protons (and electrons) helps us know how electrons are distributed among the outer shell. The periodic table is arranged in columns and rows based on the number of electrons and where these electrons are located. Take a closer look at the some of the elements in the table’s far right column in [link] . The group 18 atoms helium (He), neon (Ne), and argon (Ar) all have filled outer electron shells, making it unnecessary for them to share electrons with other atoms to attain stability; they are highly stable as single atoms. Their non-reactivity has resulted in their being named the inert gases (or noble gases ). Compare this to the group 1 elements in the left-hand column. These elements, including hydrogen (H), lithium (Li), and sodium (Na), all have one electron in their outermost shells. That means that they can achieve a stable configuration and a filled outer shell by donating or sharing one electron with another atom or a molecule such as water. Hydrogen will donate or share its electron to achieve this configuration, while lithium and sodium will donate their electron to become stable. As a result of losing a negatively charged electron, they become positively charged ions . Group 17 elements, including fluorine and chlorine, have seven electrons in their outmost shells, so they tend to fill this shell with an electron from other atoms or molecules, making them negatively charged ions. Group 14 elements, of which carbon is the most important to living systems, have four electrons in their outer shell allowing them to make several covalent bonds (discussed below) with other atoms. Thus, the columns of the periodic table represent the potential shared state of these elements’ outer electron shells that is responsible for their similar chemical characteristics.

Questions & Answers

Parkinson's disease is a caused by the degeneration of neurons that release
birabwa Reply
why is it so hard to get to the questions
Eric Reply
why is it so hard to get to questions?
Eric
what types of proteins which are found in hair,hooves and tendons?
Kapalu Reply
what is blood cells
Isaac Reply
It's cells of the blood
Kaique
can biology be also be define has a scientific study that deal with life?
Stanley Reply
do you care asking you a question
Afolayan Reply
name the gas that diffuses into the plants leaves on a bright, sunny day
Tuhemwe Reply
explain why this gas diffuses into the plant's leaves
Tuhemwe
name two gases that diffuses out of the plant's leaves on a bright sunny day
Tuhemwe
Biology olympaid
Khan
what is ecosystem
Rondy Reply
why does a car move yet it is not a living thing?
Sserujja
this is because of the engine and fuel placed on
Gift
I also think it because force has been apply to it.
Stanley
It is aplace where organísms live and associate with each other.
Nasib
what is the reason of swelling due to fracture
Ejaz Reply
Sngy alaka
Khan
how do animals reproduce
Kelvin Reply
be specific because there are so many types of animals and how they reproduce are different
Sheillah
yeah
Chinwendu
just be specific with a particular animal
Stanley
what happens when you sneeze
Asuquo Reply
The sneeze center sends out a signal to tightly close your throat, eyes and mouth. Your chest muscles contract and compress your lungs while your throat muscles relax. All of that means air, saliva and mucus is forced out of your nose and mouth. AAAAAHHHH-CHOOOO.
Hassan
how are you
Ayouba
hy
Ejaz
hii
Ishitha
hello
mahesha
Hello
Madu
Am fine
Abavon
how far
Abavon
hello
Sheillah
with why
Sheillah
with what
Sheillah
I have a question plzz
Sheillah
what is globsl warming
Rondy
Global warming is the overall rise in temperature of the Earth itself which is caused by multiple factors. Such factors include: greenhouse gases, the burning of fossil fuels and other forms of human activity.
Maryam
It's overall effects are known as climate change.
Maryam
thanks
Rondy
good
Haider
No problem.
Maryam
Thank you.
Maryam
what is creatinine?
Haider
Creatinine is a waste product produced in the body during muscle metabolism. This waste product is expelled from the body through urine. Here is it's formula:  C4H7N3O
Maryam
Formula: C4H7N3O
Maryam
ok
Haider
ok
Stephen
Outline the process of cell in the body interms of it's function.
Aliruku Reply
what communication method used mainly by plants
Jerda Reply
what is biology
james Reply
Biology is the study of life
Omoloju
yah
John
Biology is natural science that studies life and living orgasms.
Hilda
any questions from colleague
Sheillah
define nerve impulse
Karlin Reply
A nerve impulse is the way nerve cells (neurons) communicate with one another. Nerve impulsesare mostly electrical signals along the dendrites to produce a nerve impulse or action potential. The action potential is the result of ions moving in and out of the cell.
Sam

Get the best Biology course in your pocket!





Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask