MAterial Properties
Curriculum:
- Distinguish between elements, compounds and mixtures.
- Explain the idea of compounds.
- Understand that elements are made of atoms.
- Give chemical symbols for the first twenty elements of the Periodic Table.
- Compare the structures of the first twenty elements of the Periodic Table.
- Describe the structure of an atom and learn about the methods and discoveries of Rutherford.
- Describe everyday materials and their chemical properties.
- Distinguish between metals and non-metals.
- Describe and explain the differences between metals and non- metals.
- Describe trends in groups and periods.
- Name some common compounds including oxides, hydroxides, chlorides, sulfates and carbonates.
- Talk about the contribution of scientists. Secondary sources can be used.
Substances
Atoms
Chemists have investigated the structure of matter and discovered that matter is composed of small particles called atoms. As new apparatus was developed, scientists were able unravel the structure of these atoms.
Dalton
From own observations and work of other scientists, John Dalton put together his own atomic theory, which suggested that all matter was composed of tiny particles called atoms. He went on suggesting these particles could not be divided up into smaller particles and that all atoms had different masses and properties, but all atoms of the same element had the same properties and mass. Finally, his theory suggested that these atoms could be combined to form compounds.
Chemists have investigated the structure of matter and discovered that matter is composed of small particles called atoms. As new apparatus was developed, scientists were able unravel the structure of these atoms.
Dalton
From own observations and work of other scientists, John Dalton put together his own atomic theory, which suggested that all matter was composed of tiny particles called atoms. He went on suggesting these particles could not be divided up into smaller particles and that all atoms had different masses and properties, but all atoms of the same element had the same properties and mass. Finally, his theory suggested that these atoms could be combined to form compounds.
Ernest Rutherford
Top: expected results according to Thomson. Bottom: Observed results by Rutherford
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Rutherford
Research on the atoms went on and with new apparatus it was discovered that atoms were composed of electrons, which have a negative charge, and small positively charged particles. The atomic model at that point in history was devised by Thomson, who suggested that atoms were composed of a soft center of electrons with a positive ‘pudding’ around it. Ernest Rutherford tested this theory by firing positively charged alpha particles at a gold sheet, theorizing that if the atom was indeed composed of soft these particles would pass through the atoms and be detected on the sheet behind it. However, a small part of the particles were reflected and scattered all over the sheet. This disproved the ‘pudding’-theory and Rutherford theorized that there was something was repelling the alpha particles. He concluded that the nucleus of the atom had to be positive, which was surrounded by the negative electrons. According to his theory, there had to a lot of space between the nucleus and the electrons though, because most of the alpha particles did not collide with anything and were shot straight through the atom. Rutherford also theorized there were other neutral particles present in the nucleus, which were later discovered and named neutrons. Nicolas Bohr further updated the atomic model to the model that is currently accepted by the scientific community. |
Bohr Model
The Bohr model is comprised of a nucleus with protons (positively charged) and neutrons (no charge) and one or more shells with electrons (negatively charged). The number of protons is equal to the atomic number, which can be found in the table on the right. Number of protons = atomic number Electrons have a very small mass, which therefor can be neglected so the mass of an atom is comprised of the mass of the proton and neutrons in it. Since the number of protons is set for every type of atom, the rest of the mass in the atom consists entirely of neutrons. Subtracting the number of protons from the atomic mass therefor results in the number of neutrons. Number of neutrons = atomic mass – number of protons A type of atom can have different atomic masses, which means they have a different number of neutrons. If atoms from the same type of atom have a different atomic mass they are called isotopes. The most common example is carbon, which has isotopes with an atomic mass of 12 u and 13 u (and even 14 u). Even though an atom is comprised of charged particles, the atom itself is neutral. That means that the total positive charge of the protons has to be compensated by negative charge. An electron has the exact opposite charge of a proton. In other words, it has a charge, which is just as large as the charge of the proton, but instead of the charge being positive, it is negative. This means that one protons’ charge can be compensated by the charge of one electron. So the number of electrons is equal to the number of protons. Number of electrons = number of protons As stated above, these electrons are located in shells around the nucleus of the atom. Each shell of electrons has a maximum number of electrons it can hold before a new shell is formed. The first shell (closest to the nucleus) can contain up to 2 electrons, and the second shell up to 8 electrons. The other shells can contain even more electrons, but you do not have to worry about them. You might have to draw a third and forth electron shell though, but the outer electron shell of an atom can contain up to 8 electrons. Therefor if an atom has 20 electrons, which is the case for calcium, the first shell would be filled with 2 electrons, the second with 8 electrons and you might want to fill the third shell with 10 electrons. However, as described above, the outer shell of an atom can contain up to 8 electrons, so after filling the shell with 8 electrons, the remaining 2 electrons can not be added and another shell has to be added to the atom to store the last 2 electrons in. Although this technically is not correct, you might just want to learn the table below, since you only have to learn about the first 20 types of atoms. Please note that, it applies to the first 20 types of atoms, but after that the rules for filling the electron shells change. The Bohr model has been updated with quantum theories and experiments proving the existence of smaller particles of which the protons and neutrons are composed, like the recent confirmation of the Higgs boson. |
The Bohr model of aluminium
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Molecules
Atoms of non-metals can combine by forming covalent bonds between the atoms, forming a molecule. Both atoms share one covalence electron from its outer electron shell, which together form a covalent bond. In structural formulas, covalent bonds are represented by a line between the atoms.
Elements
An element is a chemical substance consisting of one type of atom. An example is a pure metal, e.g. gold, but also a molecule with just one type of atom, e.g. oxygen, O2, or nitrogen, N2. As long as the substance is pure and is consisting of one type of atom, it is considered an element.
The periodic table of elements shows every known type of atom, but does not list every element. The atom type oxygen for instance, can be used to form both oxygen gas, O2, and ozone, O3, which are both elements.
Compounds
A compound is a chemical substance consisting of more than one type of atom. These include molecules, e.g. H2O, salts (consisting of metals and non-metals), e.g. NaCl, and more complex compounds.
Mixtures
A mixture is a system in which different chemical substances are mixed. They have not reacted with each other and are therefor not chemically combined. For example, multiple compounds can be combined like dissolving salt in water. The salt did not react with water, therefor it did not for a new compound and it is not chemically combined, but the salt and water are mixed together.
Chemical properties
Chemical substances can be distinguished by their chemical properties. The properties of every substance are unique, although the difference with other substances might be small. Examples of chemical properties are:
Atoms of non-metals can combine by forming covalent bonds between the atoms, forming a molecule. Both atoms share one covalence electron from its outer electron shell, which together form a covalent bond. In structural formulas, covalent bonds are represented by a line between the atoms.
Elements
An element is a chemical substance consisting of one type of atom. An example is a pure metal, e.g. gold, but also a molecule with just one type of atom, e.g. oxygen, O2, or nitrogen, N2. As long as the substance is pure and is consisting of one type of atom, it is considered an element.
The periodic table of elements shows every known type of atom, but does not list every element. The atom type oxygen for instance, can be used to form both oxygen gas, O2, and ozone, O3, which are both elements.
Compounds
A compound is a chemical substance consisting of more than one type of atom. These include molecules, e.g. H2O, salts (consisting of metals and non-metals), e.g. NaCl, and more complex compounds.
Mixtures
A mixture is a system in which different chemical substances are mixed. They have not reacted with each other and are therefor not chemically combined. For example, multiple compounds can be combined like dissolving salt in water. The salt did not react with water, therefor it did not for a new compound and it is not chemically combined, but the salt and water are mixed together.
Chemical properties
Chemical substances can be distinguished by their chemical properties. The properties of every substance are unique, although the difference with other substances might be small. Examples of chemical properties are:
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Metals
While nonmetal materials comprised of molecules that have no charge, metals are comprised of metal ions, with some free electrons stabilizing the positive charges of the ions and ensuring they ions stay together to form a solid metal. This gives the metal ions more movability then the nonmetals, which ensures they have a wide range of physical properties that nonmetal materials do not have. Examples are listed below.
Metals are malleable and ductile, while (solid) nonmetals are brittle and not ductile. Because the small metal particles are able to move more freely, we are enabled to deform the metals.
Metals are good conductors of both heat and electricity, while nonmetals are not. Again because of the mobility of the metal particles they are better conductors. The metals also contain charged particles, which is required to conduct electricity. Compounds for example do not contain charged particles.
Metals are shiny because they absorb less light then nonmetals. Most light is reflected of their free electrons.
Metals have high boiling points because the metal ions are bonded strongly together by the free electrons. Many molecules have a bond between them that is not as strong and will therefor have a lower boiling point, although there are exceptions.
While nonmetal materials comprised of molecules that have no charge, metals are comprised of metal ions, with some free electrons stabilizing the positive charges of the ions and ensuring they ions stay together to form a solid metal. This gives the metal ions more movability then the nonmetals, which ensures they have a wide range of physical properties that nonmetal materials do not have. Examples are listed below.
Metals are malleable and ductile, while (solid) nonmetals are brittle and not ductile. Because the small metal particles are able to move more freely, we are enabled to deform the metals.
Metals are good conductors of both heat and electricity, while nonmetals are not. Again because of the mobility of the metal particles they are better conductors. The metals also contain charged particles, which is required to conduct electricity. Compounds for example do not contain charged particles.
Metals are shiny because they absorb less light then nonmetals. Most light is reflected of their free electrons.
Metals have high boiling points because the metal ions are bonded strongly together by the free electrons. Many molecules have a bond between them that is not as strong and will therefor have a lower boiling point, although there are exceptions.
The Periodic Table
The periodic table was devised by Dimitri Mendeleev. Although his assumptions were not entirely correct, it laid the groundwork for the currently used periodic table. He recognized similar properties between types of atoms and put these types of atoms together in horizontal groups in the periodic table. This means that types of atoms in the same group in the periodic table have similar, but not exactly the same, properties. The periodic table is also sorted by atomic number, which increases from left to right in every horizontal period, continuing in the group 1 of the period below after group 18 is filled.
The periodic table was devised by Dimitri Mendeleev. Although his assumptions were not entirely correct, it laid the groundwork for the currently used periodic table. He recognized similar properties between types of atoms and put these types of atoms together in horizontal groups in the periodic table. This means that types of atoms in the same group in the periodic table have similar, but not exactly the same, properties. The periodic table is also sorted by atomic number, which increases from left to right in every horizontal period, continuing in the group 1 of the period below after group 18 is filled.
Group 1 – Alkali metals
Every type of atom in group 1, with the exception of hydrogen, is an alkali metal. These metal react strongly with water, which produces a metal hydroxide and hydrogen gas. They also react vigorously with elements from group 17, the halogen. The reactivity of the alkali metals increases when going down in the periodic table.
Group 2 – Alkaline earth metals
The alkaline earth metals also react with water, with the exception of beryllium, but the reaction is not as strong as the reaction of the alkali metal with water.
Group 17 – Halogens
Sometimes reported as group 7, the halogens are among the most reactive types of atoms. Their reactivity decreases while going down in the periodic table
Group 18 – Noble gases
Sometimes reported as group 8, the noble gasses are very unreactive, which makes them inflammable, since they also do not react with oxygen.
Every type of atom in group 1, with the exception of hydrogen, is an alkali metal. These metal react strongly with water, which produces a metal hydroxide and hydrogen gas. They also react vigorously with elements from group 17, the halogen. The reactivity of the alkali metals increases when going down in the periodic table.
Group 2 – Alkaline earth metals
The alkaline earth metals also react with water, with the exception of beryllium, but the reaction is not as strong as the reaction of the alkali metal with water.
Group 17 – Halogens
Sometimes reported as group 7, the halogens are among the most reactive types of atoms. Their reactivity decreases while going down in the periodic table
Group 18 – Noble gases
Sometimes reported as group 8, the noble gasses are very unreactive, which makes them inflammable, since they also do not react with oxygen.
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Common compounds
You will have to be able to recognize certain common compounds. These compounds are listed on the left and you can find an example below. Example: a compound with molecular formula Na2SO4 has a SO4 group in the molecular formula and therefor is classified as a sulfate. The name of the compound is sodiumsulfate. |
