lesson 1
Atoms
Elements
Compounds
Carbon Dioxide Compounds :
Chemical symbols
Each element is given its own chemical symbol, like H for hydrogen or O for oxygen. Chemical symbols are usually one or two letters long.
Symbols and names
Chemical formulae
Formula and formulae
Numbers in formulae
The formula for a substance is always the same
Molecules and formulae
Molecules of elements
Molecules of compounds
Everything is made from atoms, including you. Atoms are tiny particles that are far too small to see, even with a microscope. If people were the same size as atoms, the entire population of the world would fit into a box about a thousandth of a millimetre across.We usually imagine atoms as being like tiny balls,To make diagrams simpler we often draw atoms as circles:
There are over a hundred different elements. The atoms in a particular element are the same as each other, and they are different from the atoms of all other elements. For example, lead and gold are elements. A piece of pure gold contains only gold atoms. A piece of pure lead contains only lead atoms.
The atoms of some elements do not join together, but instead they stay as separate atoms. Helium is like this. The atoms of other elements, such as hydrogen and oxygen, join together to make molecules .example of Elements:
Oxygen :
A compound is a substance that contains atoms of two or more different elements, and these atoms are chemically joined together. For example, water is a compound of hydrogen and oxygen. Each of its molecules contains two hydrogen atoms and one oxygen atom. There are very many different compounds.
Water Compound :
Every chemical symbol starts with a capital letter, with the second letter written in lower case.
For example, Mg is the correct symbol for magnesium, but mg, mG and MG are wrong. Take care to write chemical symbols correctly.
Sometimes it is easy to tell which element a symbol stands for. For example, C stands for carbon and Li stands for lithium.
But sometimes the symbol comes from a name for the element that is not an English word. For example, W stands for tungsten (from the word wolfram) and Na stands for sodium (from the word natrium).
The same chemical symbols are used all over the world, no matter which language is spoken, which makes them very useful.
Remember that we use chemical symbols to stand for the elements. For example, C stands for carbon, O stands for oxygen, S stands for sulfur and Na stands for sodium. For a molecule, we use the chemical symbols of the atoms it contains to write down its formula. For example, the formula for carbon monoxide is CO. It tells you that each molecule of carbon monoxide consists of one carbon atom joined to one oxygen atom.
Take care when writing your symbols and formulae. Be careful about when to use capital letters. For example, CO means a molecule of carbon monoxide but Co is the symbol for cobalt (an element).
The word 'formulae' is the plural of 'formula'. If we have more than one formula, we don't say formulas, we say formulae.
We use numbers to show when a molecule contains more than one atom of an element. The numbers are written below the element symbol. For example, CO2 is the formula for carbon dioxide. It tells you that each molecule has one carbon atom and two oxygen atoms.
Take care when writing these formulae. The small numbers go at the bottom. For example CO2 is correct but CO2 is wrong.
Some formulae are more complicated. For example, the formula for sodium sulfate is Na2SO4. It tells you that sodium sulfate contains two sodium atoms (Na2), one sulfur atom (S) and four oxygen atoms (O4).
All compounds have a definite composition. For example, a water molecule always contains two hydrogen atoms and one oxygen atom. It cannot be a water molecule if it has different numbers of these atoms. The formula for water is always H2O.
Oxygen is an element. All its atoms are oxygen atoms. However, they do not exist separately. Instead, they pair up to form oxygen molecules (O2). Hydrogen also has molecules with two atoms (H2). We show this in their chemical formulae.
Oxygen
Hydrogen
Compounds are made from two or more atoms chemically joined together. For example, water is a compound of hydrogen and oxygen. Each water molecule contains two hydrogen atoms and one oxygen atom. We show this in its chemical formula, H2O.
Water
Carbon dioxide
Ethanol
20 komentar
Komentar ini telah dihapus oleh pengarang.
BalasHapusnice question.A molecule is formed when two or more atoms join together chemically. A compound is a molecule that contains at least two different elements. All compounds are molecules but not all molecules are compounds.
HapusWhat are the specific differences between homogeneous and heterogeneous mix mix??
BalasHapus• Homogeneous Mixture (homo means sameness)
HapusThe ratio of solute to solvent remains the same throughout the solution
•Heterogeneous Mixture (hetero means Different)
Consists of visibly different substances or phases
why a perfume into the homogeneous mixture examples ?
BalasHapusPerfume is a fragrance that is made from a mixture of aromatic compounds and solvents. it is made by diluting perfume oils in ethanol or a mixture of ethanol and water.
HapusA homogeneous mixture has the same composition of elements and / or compounds throughout. If you observed a homogeneous mixture under a microscope, you would see that the particles of various components are evenly distributed. A homogeneous mixture is also called a solution.
so you see perfumes are homogeneous mixtures.
not all of the atom can be a compound, if not all of the atom could be a moleculle?
BalasHapus@hudiahudhud
Please explain the atom model expressed by dalton?
BalasHapusJohn Dalton proposed that all matter is composed of very small things which he called atoms. This was not a completely new concept as the ancient Greeks (notably Democritus) had proposed that all matter is composed of small, indivisible (cannot be divided) objects. When Dalton proposed his model electrons and the nucleus were unknown.
HapusImage
Why atoms c can form carbon compounds very much in nature?
BalasHapusbecause its atoms can bond to each other to a practically unlimited degree. This is possible because of carbon’s electron configuration. To understand how this is so, it is important to touch on orbital theory. Empirical data proves that atomic orbitals hybridize to form molecular orbitals.
Hapuscan you explain about All compounds have a definite composition?
BalasHapusThe law of definite composition states that chemical compounds are composed of a fixed ratio of elements as determined by mass.
HapusWhy in chemical symbol must be capital word in first word?
BalasHapusbecause its decision from IUPAC
HapusWhy living things can be regarded as atoms?
BalasHapusbecause atom form together and makes a system thats makes atom can form a living things
HapusKomentar ini telah dihapus oleh pengarang.
BalasHapusKomentar ini telah dihapus oleh pengarang.
BalasHapusPlease explain about molecules of compounds
BalasHapus