![]() ![]() (See Figure 3.4 “The Structure of the Atom”.) Figure 3.4 “The Structure of the Atom.” Atoms have protons and neutrons in the centre, making the nucleus, while the electrons orbit the nucleus. The electrons are outside the nucleus and spend their time orbiting in space about the nucleus. The relatively massive protons and neutrons are collected in the centre of an atom, in a region called the nucleus of the atom (plural nuclei). Experiments by Ernest Rutherford in England in the 1910s pointed to a nuclear model of the atom. How are these particles arranged in atoms? They are not arranged at random. Table 3.7 Properties of the Three Subatomic Particles Name Table 3.7 “Properties of the Three Subatomic Particles” summarizes the properties of these three subatomic particles. ![]() We now know that all atoms of all elements are composed of electrons, protons, and (with one exception) neutrons. The neutron is a subatomic particle with about the same mass as a proton but no charge. The proton is a more massive (but still tiny) subatomic particle with a positive charge, represented as p +. Later, two larger particles were discovered. It is often represented as e −, with the right superscript showing the negative charge. The first part to be discovered was the electron, a tiny subatomic particle with a negative charge. These concepts form the basis of chemistry.Īlthough the word atom comes from a Greek word that means “indivisible,” we understand now that atoms themselves are composed of smaller parts called subatomic particles. Atoms combine in whole-number ratios to form compounds.Atoms of the same element are the same atoms of different elements are different.The concept that atoms play a fundamental role in chemistry is formalized by the modern atomic theory, first stated by John Dalton, an English scientist, in 1808. Atoms are so small that it is difficult to believe that all matter is made from atoms-but it is. The period at the end of a printed sentence has several million atoms in it. It would take about fifty million atoms in a row to make a line that is 1 cm long. For example, it cannot explain the differences in the properties of the two carbon allotropes – diamond and graphite.The smallest piece of an element that maintains the identity of that element is called an atom. For example, argon and calcium have an atomic mass of approximately 40 amu.ĭalton’s theory could not explain the different allotropes of the same element. However, it was found that even atoms of different elements can have the same mass. For example, hydrogen, deuterium, and tritium are isotopes with different masses.ĭalton states that atoms of different elements can have different masses. However, it was later established that atoms of the same element can have different masses. However, we know an atom consists of electron, proton, and neutron.ĭalton states that atoms of a given element have precisely the same masses. Does not account for subatomic particlesĭalton stated that atoms are indivisible and cannot be further divided. While Dalton’s atomic theory laid the path toward the fundamental understanding of atoms and matter, it had a few demerits. ![]() However, both the sodium and chlorine atoms still exist. In the above example, sodium and chlorine combine to make salt. A chemical reaction is a rearrangement of atoms.ĭalton suggested that chemical reactions neither destroy nor create atoms. When they react, the Na and Cl atoms combine in a 1:1 ratio to form white crystals of sodium chloride (NaCl).Ĥ. The other is chlorine (Cl), which is a gas. One is sodium (Na), which is a highly reactive metal. For example, household common salt comprises two elements with varying physical and chemical properties. Compounds are formed from the combinations of two or more different types of atoms.ĭalton proposed that compounds comprise two or more atoms of different types. For example, an oxygen atom is different from a carbon atom.ģ. However, no two elements can have the same set of properties. Elements may share similar properties like boiling and melting points and electronegativity. All atoms of a given element are identical in mass and properties.ĭalton proposed that every single atom of a specific element is the same as that of every other element. Dalton proposed that all matter is made of tiny indivisible atoms, which he imagined as “solid and movable particles”.Ģ. The laws of conservation of mass and definite proportions can be explained using the concept of atoms. ![]()
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