Selenium Valence Electrons

Posted on 01-05-2021 by admin

Indeed, the toxicity level of selenium to humans was established only 20 years ago by studies of Chinese victims of selenium poisoning, selenosis, who grew corn on selenium rich coal rocks. Selenosis has some lovely symptoms: a garlic odor on the breath, hair loss, sloughing of nails, fatigue, irritability, and eventually cirrhosis of the liver.

Element Selenium - Se

Selenium has six valence electrons. What is the valence of selenium. The number of valence electrons plus the valence equals the. The sum minus the. He valence of selenium depends on which compound it is in. Selenium is very similar to sulfur. It may have a valence of 6; example selenium hexafluoride SeF6, selenium trioxide SeO3 4; example selenium tetrafluoride SeF4, selenium dioxide SeO2 2; example selenium difluoride SeF2, selenium dichloride SeCl2 and - 2; example hydrogen selenide H2Se. Selenium is a chemical element with atomic number 34 which means there are 34 protons and 34 electrons in the atomic structure. The chemical symbol for Selenium is Se. Selenium is a nonmetal with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic.

Comprehensive data on the chemical element Selenium is provided on this page; including scores of properties, element names in many languages, most known nuclides of Selenium. Common chemical compounds are also provided for many elements. In addition technical terms are linked to their definitions and the menu contains links to related articles that are a great aid in one's studies.

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Overview of Selenium

Atomic Number: 34
Group: 16
Period: 4
Series: Nonmetals

Selenium's Name in Other Languages

Latin: Selenium
Czech: Selen
Croatian: Selenij
French: Sélénium
German: Selen - r
Italian: Selenio
Norwegian: Selen
Portuguese: Selênio
Russian: Селен
Spanish: Selenio
Swedish: Selen

Atomic Structure of Selenium

Atomic Radius: 1.22Å
Atomic Volume: 16.45cm³/mol
Covalent Radius: 1.16Å
Cross Section (Thermal Neutron Capture) σ_a/barns: 11.7
Crystal Structure: Hexagonal
Electron Configuration:
1s² 2s²p⁶ 3s²p⁶d¹⁰ 4s²p⁴
Electrons per Energy Level: 2,8,18,6
Shell Model
Ionic Radius: 0.5Å
Filling Orbital: 4p⁴
Number of Electrons (with no charge): 34
Number of Neutrons (most common/stable nuclide): 45
Number of Protons: 34
Oxidation States: ±2,4,6
Valence Electrons: 4s²p⁴
Electron Dot Model

Chemical Properties of Selenium

Electrochemical Equivalent: 0.7365g/amp-hr
Electron Work Function: 5.9eV
Electronegativity: 2.55 (Pauling); 2.48 (Allrod Rochow)
Heat of Fusion: 6.694kJ/mol
Incompatibilities:
Acids, strong oxidizers, chromium trioxide, potassium bromate, cadmium
Ionization Potential
- First: 9.752
- Second: 21.19
- Third: 30.82
Valence Electron Potential (-eV): 120

Physical Properties of Selenium

Atomic Mass Average: 78.96
Boiling Point: 958K 685°C 1265°F
Coefficient of lineal thermal expansion/K^-1: 36.9E^-6
Conductivity
Electrical: 1.0E^-12 10⁶/cm Ω
Thermal: 0.0204 W/cmk
Density: 4.79g/cc @ 300K
Description:
Dark gray lustrous rods or dark red crystals of non-metal. Burns in contact with air but is unaffected by water. Disolves in alkalis and concentrated HNO₃.
Elastic Modulus:
- Bulk: 8.3/GPa
- Rigidity: 3.7/GPa
- Youngs: 58/GPa
Enthalpy of Atomization: 205.9 kJ/mole @ 25°C
Enthalpy of Fusion: 6.69 kJ/mole
Enthalpy of Vaporization: 26.3 kJ/mole
Flammablity Class: Combustible Solid
Freezing Point:see melting point
Hardness Scale
- Brinell: 736 MN m^-2
- Mohs: 2
Heat of Vaporization: 37.7kJ/mol
Melting Point: 494K 221°C 430°F
Molar Volume: 16.42 cm³/mole
Optical Refractive Index: 1.000895
Physical State (at 20°C & 1atm): Solid
Specific Heat: 0.32J/gK
Vapor Pressure = 0.695Pa@221°C

Regulatory / Health

CAS Number
- 7782-49-2 powder
UN/NA ID and ERG Guide Number
- 2658 / 152 powder
RTECS: VS7700000
OSHAPermissible Exposure Limit (PEL)
- TWA: 0.2 mg/m³
OSHA PEL Vacated 1989
- TWA: 0.2 mg/m³
NIOSHRecommended Exposure Limit (REL)
- TWA: 0.2 mg/m³
- IDLH: 1 mg/m³
Routes of Exposure: Inhalation; Ingestion; Skin and/or eye contact
Target Organs: Eyes, skin, respiratory system, liver, kidneys, blood, spleen
Levels In Humans:
Note: this data represents naturally occuring levels of elements in the typical human, it DOES NOT represent recommended daily allowances.
- Blood/mg dm^-3: 0.171
- Bone/p.p.m: 1-9
- Liver/p.p.m: 0.35-2.4
- Muscle/p.p.m: 0.42-1.9
- Daily Dietary Intake: 0.006-0.2 mg
- Total Mass In Avg. 70kg human: 10-65 mg

Who / Where / When / How

Discoverer: Jöns J. Berzelius
Discovery Location: Stockholm Sweden
Discovery Year: 1817
Name Origin:
Greek: Selênê (Moon)
Abundance of Selenium:
- Earth's Crust/p.p.m.: 0.05
- Seawater/p.p.m.:
  - Atlantic Suface: 4.6E-08
  - Atlantic Deep: 1.8E-07
  - Pacific Surface: 1.5E-08
  - Pacific Deep: 1.65E-07
- Atmosphere/p.p.m.: N/A
- Sun (Relative to H=1E¹²): N/A
Sources of Selenium:
Obtained as a by-product of lead, copper and nickel refining. World wide annual production is around 600 tons. Primary mining areas are Canada, USA, Bolivia and Russia.
Uses of Selenium:
Used in photoelectric cells, TV cameras, as a semiconductor in solar batteries, light meters, copy machines, anti-dandruff shampoo and rectifiers. Also colors glass red.
Additional Notes:
A dose of selenium as small as 5 mg per day can be lethal for many humans.

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References

A list of reference sources used to compile the data provided on our periodic table of elements can be found on the main periodic table page.

Related Resources

Anatomy of the Atom
Answers many questions regarding the structure of atoms.
Molarity, Molality and Normality
Introduces stoichiometry and explains the differences between molarity, molality and normality.
Molar Mass Calculations and Javascript Calculator
Molar mass calculations are explained and there is a JavaScript calculator to aid calculations.
Chemical Database
This database focuses on the most common chemical compounds used in the home and industry.

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Kenneth Barbalace. Periodic Table of Elements - Selenium - Se. EnvironmentalChemistry.com. 1995 - 2021. Accessed on-line: 4/24/2021
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Selenium Number Valence Electrons

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3.1 Two Types of Bonding

Learning Objectives

Define the octet rule.
Describe how ionic bonds are formed.

Atoms can join together by forming a chemical bondA very strong attraction between two atoms., which is a very strong attraction between two atoms. Chemical bonds are formed when electrons in different atoms interact with each other to make an arrangement that is more stable than when the atoms are apart.

What causes atoms to make a chemical bond with other atoms, rather than remaining as individual atoms? A clue comes by considering the noble gas elements, the rightmost column of the periodic table. These elements—helium, neon, argon, krypton, xenon, and radon—do not form compounds very easily, which suggests that they are especially stable as lone atoms. What else do the noble gas elements have in common? Except for helium, they all have eight valence electrons. Chemists have concluded that atoms are especially stable if they have eight electrons in their outermost shell. This useful rule of thumb is called the octet ruleThe idea that atoms tend to have eight electrons in their valence shell., and it is a key to understanding why compounds form.

Note

Of the noble gases, only krypton, xenon, and radon have been found to make compounds.

There are two ways for an atom that does not have an octet of valence electrons to obtain an octet in its outer shell. One way is the transfer of electrons between two atoms until all atoms have octets. Because some atoms will lose electrons and some atoms will gain electrons, there is no overall change in the number of electrons, but individual atoms acquire a nonzero electric charge. Those that lose electrons become positively charged, and those that gain electrons become negatively charged. Charged atoms are called ionsA charged atom.. Because opposite charges attract (while like charges repel), these oppositely charged ions attract each other, forming ionic bondsAn attraction between oppositely charged ions.. The resulting compounds are called ionic compoundsA compound formed with an ionic bond. and are the primary subject of this chapter.

The second way for an atom to obtain an octet of electrons is by sharing electrons with another atom. These shared electrons simultaneously occupy the outermost shell of more than one atom. The bond made by electron sharing is called a covalent bond. Covalent bonding and covalent compounds will be discussed in Chapter 4 'Covalent Bonding and Simple Molecular Compounds'.

Note

Despite our focus on the octet rule, we must remember that for small atoms, such as hydrogen, helium, and lithium, the first shell is, or becomes, the outermost shell and hold only two electrons. Therefore, these atoms satisfy a “duet rule” rather than the octet rule.

Example 1

A sodium atom has one valence electron. Do you think it is more likely for a sodium atom to lose one electron or gain seven electrons to obtain an octet?

Solution

Although either event is possible, a sodium atom is more likely to lose its single valence electron. When that happens, it becomes an ion with a net positive charge. This can be illustrated as follows:

Sodium atom		Sodium ion
11 protons	11+	11 protons	11+
11 electrons	11−	10 electrons	10−
0 overall charge	+1 overall charge

Skill-Building Exercise

A fluorine atom has seven valence electrons. Do you think it is more likely for a fluorine atom to lose seven electrons or gain one electron to obtain an octet?

Concept Review Exercises

How are ionic bonds formed?