Metalloids have some characteristics of metals and some characteristics of non-metals. Silicon and arsenic are metalloids. As of November, , elements have been identified the most recently identified was ununseptium, in Of these known elements, only the first 98 are known to occur naturally on Earth.
The elements that do not occur naturally on Earth are the synthetic products of man-made nuclear reactions. Hydrogen and helium are by far the most abundant elements in the universe. The remainder is dark matter, a mysterious substance that is not composed of chemical elements.
Dark matter lacks protons, neutrons, or electrons. Pure samples of isolated elements are uncommon in nature. Carbon is also commonly found in the form of coal, graphite, and diamonds. The noble gases e. Still, most of these elements are found in mixtures. When two distinct elements are chemically combined—i. Most elements on Earth bond with other elements to form chemical compounds, such as sodium Na and Chloride Cl , which combine to form table salt NaCl. Water is another example of a chemical compound.
Limit the number of marshmallow colours to two to reduce the number of things students need to think about related to cognitive load: rsc.
Present a range of diagrammatic representations of elements and molecules, and ask your students to identify which are elements and which are compounds.
Model your own thinking to students, demonstrating how you approach each task and use your knowledge. Download a worksheet that asks students to build representations of molecules using white and pink marshmallows word , pdf or ppt , and teacher notes word , pdf. Download a worksheet from the Education in Chemistry website for students to build representations of molecules using white and pink marshmallows, with teacher notes: rsc. Story-telling enlivens the knowledge students need, and the discovery of the elements provides rich pickings.
Ask students to think about why these ideas may have developed. Explain how phlogiston was the forerunner of oxygen , and enjoy telling students phosphorous was discovered accidently after boiling urine. Why is air a mixture? What is fire? Explain how phlogiston was the forerunner of oxygen rsc. A common misconception is that atoms share the properties of the bulk material. Emphasise how, for example, individual copper atoms have no colour, but billions of them joined together make a lustrous red metal.
Furthermore, the element symbol Cu can actually represent billions of particles in a giant structure, rather than one individual atom. A common misconception is that atoms share the properties of the bulk material rsc. Scientific keywords often have different non-scientific meanings, leading to many misconceptions.
Use graphic organisers to help students make links between words and concepts, and use low-stakes vocabulary quizzes. The act of quizzing itself aids retention, and familiarity with key language can reduce the cognitive load on working memory. This leaves students with a greater capacity for understanding the important underlying concepts. Another good starting point for this topic is to have students learn the names and symbols of the first twenty elements. Chemistry vocabulary tests or memory games are a straightforward way of aiding this memorisation.
Understanding elements and compounds is fundamental to many aspects of more advanced study. The models learnt at ages 11—14 will be extended to include types of bonding and giant lattices. Students will learn the detailed structure of atoms and how elements can be defined in terms of atomic number.
The particle model will be extended, and they will appreciate that particles can be atoms, ions or molecules. Bear in mind, as you teach this topic, that elements and compounds are often represented as molecular gases at this stage, for simplicity. If you want to stretch students, you could get them to sketch molecules in a range of states.
Add this quick demo to the end of a lesson on squeaky pops to show the dramatic impact of mixing chemicals in the correct proportions. Introduce the study of molecules containing carbon atoms to your students with these many different contexts. Observation is a key skill for budding chemists. This is how to develop it with your younger students. Site powered by Webvision Cloud.
Skip to main content Skip to navigation. No comments. Basically a molecule is like a very small group of atoms that go around together they are still too small to see.
These are then called oxygen molecules and that is why oxygen is often represented as O 2. All compounds are molecules, but not all molecules are compounds e. H 2 is a molecule because it is composed of two atoms chemically combined, but because they are both the same element hydrogen the molecule is not a compound. H 2 O is both a molecule because it is composed of two atoms and it is also a molecule because there are two different types of element involved; hydrogen and oxygen.
If a substance is made up of different components but they are just mingled together rather than combined at an atomic level then we call this a mixture.
A mixture contains two or more different substances mingled together but not chemically combined. If you pour sulphur power over iron filings and mix them together you get a mixture, and to separate them simply use a magnet which will attract the iron filings and leave the sulphur powder behind. Name and explain a method that the student could use to separate the iron from the sulphur in the iron and sulphur mixture.
Could the method of separation that you have suggested be used to separate the iron from the sulphur in the compound iron sulphide? Entire UL. Current site.
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