Subatomic particles atomic weight

Ans. (a) The nucleus is a distinct part of the atom. Neutrons are subatomic particles which, along with protons, are located in the nucleus. (b) Mass number refers to individual isotopes. It is the sum of the numbers of protons and neutrons. Atomic weight refers to the naturally occurring mixture of isotopes, and is the relative mass of the average atom compared to l2C. (/) Atomic mass is the same as atomic weight [see (b)]. Atomic mass unit is the unit of atomic weight. 

The primary subatomic particles in each atom are protons, electrons, and neutrons. The mass (weight) and charge of each are given in Table 1.1. 

See also Atomic weight Element, chemical Subatomic particles. 

The second statement needs modification, too, since today we know about subatomic particles, the particles that make up atoms. Looking only at the element, carbon, we find there are three different kinds of carbon atoms in nature, each with a slightly different composition and weight. Yet, all carbon atoms have the same chemical properties. How this can happen will be explained in this chapter. 

A firm grasp of the basic ideas of division of matter is important for the understanding of physical sciences. These basic ideas presented here are not only used in chemistry and physics, but in many diverse fields such as medicine, engineering, astronomy, geology, and so on. In this chapter, we will discuss ideas about atoms and molecules, and related aspects such as moles, Avogadro number, percentage composition, atomic mass, atomic weight, and subatomic particles. 

The atoms of different elements are different in weight, size and behaviour. Atoms are built from a number of different electrically charged or neutral subatomic particles. An atom consists of a nucleus, which contains the heavier particles, some of which are positively charged (protons) and some neutral (neutrons), and this is surrounded by a number of much lighter negatively charged particles called electrons. The electrons are in constant... 

It is not possible to state the absolute mass or weight of any material object. At the most fundamental level, one can only state that a hydrogen atom has the mass of a single proton and a single electron it is impossible to know the absolute masses of those subatomic particles. This basic relationship, however, provides the means whereby other atoms can be... 

Atoms consist of three types of subatomic particles positively charged protons and uncharged neutrons make up the nucleus, and electrons exist outside the nucleus. Atoms are neutral because the number of protons equals the number of electrons. All the atoms of an element have the same number of protons (atomic number, Z) and thus the same chemical behavior. Isotopes of an element have atoms with different masses because they have different numbers of neutrons. The atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes. (Section 2.5)... 

Once the particulate nature of matter began to evolve, it was a matter of time (over half a century) before a coherent arrangement of the different types of atoms based on their atomic weight began to take shape (Mendeleev [5]). A decade later, one of the fundamental subatomic particles was discovered, the electron (Crookes), but this discovery was not understood for what it was until Thomson [6]... 

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