Er Element

2/14/2022by admin

1-833-ERE-ASAP (1-833-373-2727) [email protected] Home; About Us; Services. Residential Renovation & Remodel. Smith Signature Premier 50-Gallon Tall 12-Year Limited 5500-Watt Double Element Electric Water Heater in the Electric Water Heaters department at Lowe's.com. Smith's Signature Premier 50-Gallon Tall Energy Smart 12-Year Limited Warranty Electric Water Heater is designed to provide efficient and reliable hot.

Chemical properties of erbium - Health effects of erbium - Environmental effects of erbium

68

Atomic mass

167.26 g.mol -1

Electronegativity according to Pauling

1.2

Density

9.2 g.cm-3 at 20°C

Melting point

1522 °C

Boiling point

2510 °C

Vanderwaals radius

unknown

Ionic radius

unknown

Isotopes

9

Electronis shell

[ Xe ] 4f12 6s2

Energy of first ionisation

587.6 kJ.mol -1

Energy of second ionisation

1149 kJ.mol -1

Standard potential

- 2.30 V

Discovered by

Carl Mosander in 1843

Erbium

Erbium is a soft, malleable, lustrous, silvery metal. It is very stable in air, it reacts very slowly with oxygen and water and dissolves in acids. Its salts are rose coloured and it has a sharp adsorption spectra in visible, ultraviolet and infrared light.

Applications

Some erbium is added to alloys with metals such vanadium because it lowers their hardness, making them more workable. Due to its adsorption of infrared light, erbium is added to the glass of special safety spectacles for workers, such as welders and glass-blowers. It is used as a photographic filter as well, and to dope optical fibers at regular intervals to amplify signals. Finally, due to its pink colour, erbium is sometimes used as a glass and porcelain enamel glaze colorant.

Erbium in the environment

Erbium is never found as a free element in nature. It is found in minerals that include all the rare-earth elements. Erbium is one of the more abundant rare-earth elements. The main mining areas are China and US. The most important ores are monazite and bastanite, were it is present in extrable amounts. Better suorces of the element are xenotime and euxenite. World production of erbium is 500 tonnes per year.

Health effects of erbium

Erbium has no biological role even if it has been noted that it stimulates metabolism. It is difficult to determine the amount of erbium present in the human body. The levels are highest in bones, with smaller amounts being present in the liver and kidneys.

Environmental effects of erbium

Erbium poses no environmental threat to plants and animals.


Back to chart periodic elements

More from 'Elements'

Lenntech (European Head Office)

Distributieweg 3
2645 EG Delfgauw
The Netherlands
Phone: +31 152 610 900
fax: +31 152 616 289
e-mail: [email protected]


Lenntech USA LLC (Americas)

5975 Sunset Drive
South Miami, FL 33143
USA
Phone: +1 877 453 8095
e-mail: [email protected]


Lenntech DMCC (Middle East)

Level 5 - OFFICE #8-One JLT Tower
Jumeirah Lake Towers
Dubai - U.A.E.
Phone: +971 4 429 5853
e-mail: [email protected]


Copyright © 1998-2021 Lenntech B.V. All rights reserved

  • DBMS Tutorial
  • Entity Relationship Model
ElementEr Element
  • Relational Model
  • Relational Database Design
Number
  • Storage and File Structure
  • Indexing and Hashing
  • Transaction And Concurrency
  • Backup and Recovery
  • DBMS Useful Resources
  • Selected Reading

The ER model defines the conceptual view of a database. It works around real-world entities and the associations among them. At view level, the ER model is considered a good option for designing databases.

Entity

Element

An entity can be a real-world object, either animate or inanimate, that can be easily identifiable. For example, in a school database, students, teachers, classes, and courses offered can be considered as entities. All these entities have some attributes or properties that give them their identity.

An entity set is a collection of similar types of entities. An entity set may contain entities with attribute sharing similar values. For example, a Students set may contain all the students of a school; likewise a Teachers set may contain all the teachers of a school from all faculties. Entity sets need not be disjoint.

Attributes

Entities are represented by means of their properties, called attributes. All attributes have values. For example, a student entity may have name, class, and age as attributes.

There exists a domain or range of values that can be assigned to attributes. For example, a student's name cannot be a numeric value. It has to be alphabetic. A student's age cannot be negative, etc.

Types of Attributes

  • Simple attribute − Simple attributes are atomic values, which cannot be divided further. For example, a student's phone number is an atomic value of 10 digits.

  • Composite attribute − Composite attributes are made of more than one simple attribute. For example, a student's complete name may have first_name and last_name.

  • Derived attribute − Derived attributes are the attributes that do not exist in the physical database, but their values are derived from other attributes present in the database. For example, average_salary in a department should not be saved directly in the database, instead it can be derived. For another example, age can be derived from data_of_birth.

  • Single-value attribute − Single-value attributes contain single value. For example − Social_Security_Number.

  • Multi-value attribute − Multi-value attributes may contain more than one values. For example, a person can have more than one phone number, email_address, etc.

These attribute types can come together in a way like −

  • simple single-valued attributes
  • simple multi-valued attributes
  • composite single-valued attributes
  • composite multi-valued attributes

Entity-Set and Keys

Er Element Definition

Key is an attribute or collection of attributes that uniquely identifies an entity among entity set.

For example, the roll_number of a student makes him/her identifiable among students.

  • Super Key − A set of attributes (one or more) that collectively identifies an entity in an entity set.

  • Candidate Key − A minimal super key is called a candidate key. An entity set may have more than one candidate key.

  • Primary Key − A primary key is one of the candidate keys chosen by the database designer to uniquely identify the entity set.

Relationship

The association among entities is called a relationship. For example, an employee works_at a department, a student enrolls in a course. Here, Works_at and Enrolls are called relationships.

Relationship Set

Er Elemento

A set of relationships of similar type is called a relationship set. Like entities, a relationship too can have attributes. These attributes are called descriptive attributes.

Degree of Relationship

The number of participating entities in a relationship defines the degree of the relationship.

  • Binary = degree 2
  • Ternary = degree 3
  • n-ary = degree

Mapping Cardinalities

Cardinality defines the number of entities in one entity set, which can be associated with the number of entities of other set via relationship set.

Er Elementary School

  • One-to-one − One entity from entity set A can be associated with at most one entity of entity set B and vice versa.

  • One-to-many − One entity from entity set A can be associated with more than one entities of entity set B however an entity from entity set B, can be associated with at most one entity.

  • Many-to-one − More than one entities from entity set A can be associated with at most one entity of entity set B, however an entity from entity set B can be associated with more than one entity from entity set A.

  • Many-to-many − One entity from A can be associated with more than one entity from B and vice versa.

Comments are closed.