пятница, 28 марта 2014 г.
Elements
An element is a pure substance that is made from a single type of atom. Elements are the building blocks for all the rest of the matter in the world. Examples of elements include iron, oxygen, hydrogen, gold, and helium.
Atomic Number
An important number in an element is the atomic number. This is the number of protons in each atom. Each element has a unique atomic number. Hydrogen is the first element and has one proton, so it has an atomic number of 1. Gold has 79 protons in each atom and has an atomic number of 79. Elements in their standard state also have the same number of electrons as protons.
Forms of an Element
Even though elements are all made from the same type of atoms, they can still come in different forms. Depending on their temperature they can be solid, liquid, or gas. They can also take different forms depending on how tightly the atoms are packed together. Scientists call these allotropes. One example of this is carbon. Depending on how carbon atoms fit together they can form diamond, coal, or graphite.
How many elements are there?
There are currently 118 known elements. Of these, only 94 are thought to naturally exist on Earth.
Families of Elements
Elements are sometimes grouped together because they have similar properties. Here a few of the types:
Noble Gases - Helium, neon, argon, krypton, xenon, and radon are all noble gases. They are unique in that the outer shell of their atoms is full of electrons. This means they don't react much with other elements. They are often used in signs as they glow in bright colors when an electrical current is passed through them.
Alkali Metals - These elements have just 1 electron in the outer shell of their atom and are very reactive. Some examples are lithium, sodium, and potassium.
Other groups include transition metals, nonmetals, halogens, alkali earth metals, actinides, and lanthanides.
Fun Facts about Elements
Atomic Number
An important number in an element is the atomic number. This is the number of protons in each atom. Each element has a unique atomic number. Hydrogen is the first element and has one proton, so it has an atomic number of 1. Gold has 79 protons in each atom and has an atomic number of 79. Elements in their standard state also have the same number of electrons as protons.
Forms of an Element
Even though elements are all made from the same type of atoms, they can still come in different forms. Depending on their temperature they can be solid, liquid, or gas. They can also take different forms depending on how tightly the atoms are packed together. Scientists call these allotropes. One example of this is carbon. Depending on how carbon atoms fit together they can form diamond, coal, or graphite.
How many elements are there?
There are currently 118 known elements. Of these, only 94 are thought to naturally exist on Earth.
Families of Elements
Elements are sometimes grouped together because they have similar properties. Here a few of the types:
Noble Gases - Helium, neon, argon, krypton, xenon, and radon are all noble gases. They are unique in that the outer shell of their atoms is full of electrons. This means they don't react much with other elements. They are often used in signs as they glow in bright colors when an electrical current is passed through them.
Alkali Metals - These elements have just 1 electron in the outer shell of their atom and are very reactive. Some examples are lithium, sodium, and potassium.
Other groups include transition metals, nonmetals, halogens, alkali earth metals, actinides, and lanthanides.
Fun Facts about Elements
- Elements found on Earth and Mars are exactly the same.
- Hydrogen is the most common element found in the universe. It is also the lightest element.
- Isotopes are atoms of the same element, with different numbers of neutrons.
- In ancient times the elements referred to fire, earth, water, and air.
- Helium is the second most common element in the universe, but is very rare on the Earth.
Periodic Table
The Periodic Table is a way of listing the elements. Elements are listed in the table by the structure of their atoms. This includes how many protons they have as well as how many electrons they have in their outer shell. From left to right and top to bottom, the elements are listed in the order of their atomic number, which is the number of protons in each atom.
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Why is it called the Periodic Table?
It is called "periodic" because elements are lined up in cycles or periods. From left to right elements are lined up in rows based on their atomic number (the number of protons in their nucleus). Some columns are skipped in order for elements with the same number of valence electrons to line up on the same columns. When they are lined up this way, elements in the columns have similar properties.
Each horizontal row in the table is a period. There are seven (or eight) total periods. The first one is short and only has two elements, hydrogen and helium. The sixth period has 32 elements. In each period the left most element has 1 electron in its outer shell and the right most element has a full shell.
Groups
Groups are the columns of the periodic table. There are 18 columns or groups and different groups have different properties.
One example of a group is the noble or inert gases. These elements all line up in the eighteenth or last column of the periodic table. They all have a full outer shell of electrons, making them very stable (they tend not to react with other elements). Another example is the alkali metals which all align on the left-most column. They are all very similar in that they have only 1 electron in their outer shell and are very reactive. You can see all the groups in the table below.
This lining-up and grouping of similar elements helps chemists when working with elements. They can understand and predict how an element might react or behave in a certain situation.
Element Abbreviations
Each element has its own name and abbreviation in the periodic table. Some of the abbreviations are easy to remember, like H for hydrogen. Some are a bit harder like Fe for iron or Au for gold. For gold the "Au" comes from the Latin word for gold "aurum".
Who invented it?
The original periodic table was first proposed by Russian chemist Dmitri Mendeleev in 1869.
Fun facts about the Periodic Table
It is called "periodic" because elements are lined up in cycles or periods. From left to right elements are lined up in rows based on their atomic number (the number of protons in their nucleus). Some columns are skipped in order for elements with the same number of valence electrons to line up on the same columns. When they are lined up this way, elements in the columns have similar properties.
Each horizontal row in the table is a period. There are seven (or eight) total periods. The first one is short and only has two elements, hydrogen and helium. The sixth period has 32 elements. In each period the left most element has 1 electron in its outer shell and the right most element has a full shell.
Groups
Groups are the columns of the periodic table. There are 18 columns or groups and different groups have different properties.
One example of a group is the noble or inert gases. These elements all line up in the eighteenth or last column of the periodic table. They all have a full outer shell of electrons, making them very stable (they tend not to react with other elements). Another example is the alkali metals which all align on the left-most column. They are all very similar in that they have only 1 electron in their outer shell and are very reactive. You can see all the groups in the table below.
This lining-up and grouping of similar elements helps chemists when working with elements. They can understand and predict how an element might react or behave in a certain situation.
Element Abbreviations
Each element has its own name and abbreviation in the periodic table. Some of the abbreviations are easy to remember, like H for hydrogen. Some are a bit harder like Fe for iron or Au for gold. For gold the "Au" comes from the Latin word for gold "aurum".
Who invented it?
The original periodic table was first proposed by Russian chemist Dmitri Mendeleev in 1869.
Fun facts about the Periodic Table
- Carbon is unique in that it is known to form up to 10 million different compounds. Carbon is important to the existence of life.
- Francium is the rarest element on earth. There are probably no more than a few ounces of it on earth at any given time.
- The only letter not in the periodic table is the letter J.
- The country Argentina is named after the element silver (symbol Ag) which is argentum in Latin.
- Although there is helium on Earth, it was first discovered by observing the sun.
Five famous female chemists
Cleopatra the Alchemist (dates unknown)
Not the same person as Cleopatra VII, this one lived (probably) in the 3rd or 4th century. The title Cleopatra the Alchemist is a pseudonym and her real name has been lost. She was thought to be one of only four women who knew how to make the mythical philosopher’s stone (yes, just like in Harry Potter. Well sort of) and, perhaps more scientifically, her work also contained several descriptions and drawings of the technical process of furnaces. She’s also sometimes credited with the invention of an early type of distillation apparatus. Without this useful chemical technique, we wouldn’t have petrol, plastics or, indeed, vodka. Cheers!
Not the same person as Cleopatra VII, this one lived (probably) in the 3rd or 4th century. The title Cleopatra the Alchemist is a pseudonym and her real name has been lost. She was thought to be one of only four women who knew how to make the mythical philosopher’s stone (yes, just like in Harry Potter. Well sort of) and, perhaps more scientifically, her work also contained several descriptions and drawings of the technical process of furnaces. She’s also sometimes credited with the invention of an early type of distillation apparatus. Without this useful chemical technique, we wouldn’t have petrol, plastics or, indeed, vodka. Cheers!
Marie Curie (1867-1934)
The Polish Madame Marie Curie is most famous for her work on radioactivity and is often thought of as more of a physicist. However she definitely earned her chemical chops for discovering two (count ‘em, two) whole new elements: polonium (Po) and radium (Ra). She painstakingly managed to isolate about 0.1 g of radium chloride from 1 ton (907185 g) of the mineral pitchblende. Now that’s patience. In 1948 the element curium (Cm) was named in her, and her husband Pierre’s, honour.
Elizabeth Arden (1884-1966)
A famous name, if not one we necessarily associate with science, she was born Florence Nightingale Graham and changed her name in 1909. Although not formally educated as such, she counts as a chemist for formulating, as well as manufacturing and marketing, her cosmetic products. She pioneered the idea that cosmetics could and should be scientifically formulated, a concept that many other companies subsequently copied. She did wear an awful lot of pink, but nobody’s perfect.
A famous name, if not one we necessarily associate with science, she was born Florence Nightingale Graham and changed her name in 1909. Although not formally educated as such, she counts as a chemist for formulating, as well as manufacturing and marketing, her cosmetic products. She pioneered the idea that cosmetics could and should be scientifically formulated, a concept that many other companies subsequently copied. She did wear an awful lot of pink, but nobody’s perfect.
Rosalind Franklin (1920-1958)
Who discovered the structure of DNA? Wasn’t that Watson and Crick? Actually it was x-ray crystallographer Rosalind Franklin who produced the first images of deoxyribonucleic acid, and Watson and Crick even publicly admitted to using her data to develop their hypothesis. Sadly Franklin was a cautious scientist and her work, based on experimental results, was published after their theoretical paper. Subsequently she’s often forgotten about, particularly because, as she died in 1958 and the rules forbid posthumous nominations, she was never included included in the Nobel Prize awarded to Crick, Watson and Wilkins in 1962. Don’t hide your light girls.
Who discovered the structure of DNA? Wasn’t that Watson and Crick? Actually it was x-ray crystallographer Rosalind Franklin who produced the first images of deoxyribonucleic acid, and Watson and Crick even publicly admitted to using her data to develop their hypothesis. Sadly Franklin was a cautious scientist and her work, based on experimental results, was published after their theoretical paper. Subsequently she’s often forgotten about, particularly because, as she died in 1958 and the rules forbid posthumous nominations, she was never included included in the Nobel Prize awarded to Crick, Watson and Wilkins in 1962. Don’t hide your light girls.
Anna Jane Harrison (1912-1998)
Harrison, who unlike many historical chemists (when you spend your days messing about with substances that so often turn out to be toxic, you’re invariably in danger of shuffling off this mortal coil earlier than most) managed to live until the ripe old age of 86, was an American organic chemist and the first female president of the American Chemical Society. She was also the recipient of twenty honorary degrees, none of which were bought from dodgy internet sites. She worked on toxic smoke during the second world war, and also contributed to research on ultraviolet light.
Harrison, who unlike many historical chemists (when you spend your days messing about with substances that so often turn out to be toxic, you’re invariably in danger of shuffling off this mortal coil earlier than most) managed to live until the ripe old age of 86, was an American organic chemist and the first female president of the American Chemical Society. She was also the recipient of twenty honorary degrees, none of which were bought from dodgy internet sites. She worked on toxic smoke during the second world war, and also contributed to research on ultraviolet light.
Famous Chemists
Chemistry is a study of reactions between chemicals and substances that most people experience in their everday life. All of our medicines and household products are the result of a history of chemical studies and discoveries. Below is a list of some of the most important chemists of all time organized by the significance of their contributions to this field.
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