What is the atomic number of an element

What is the atomic number of an element having a total of 5 electrons in n = 4 ... 

Starting at the first electron added to an atom, (a) what is the number of the first electron in the second shell of the atom (b) What is the atomic number of the first element of the second period (c) What is the number of the first electron in the third shell of the atom (d) What is the atomic number of the first element of the third period (e) What is the number of the first electron in the fourth shell of the atom (/) What is the atomic number of the first element of the fourth period ... 

Each element has a unique atomic number. The atomic number of an element tells you how many protons it has in its nucleus. The atomic number of chlorine, for example, is 17 this tells you that every atom of chlorine has 17 protons in its nucleus. Since there are 17 positive protons in the nucleus, there are 17 negative electrons orbiting the nucleus. The atom is electrically neutral. The number of protons never changes. No matter where a chlorine atom is found, or where it has come from, or what it is doing, or if it is in a compound with other elements, it will always have 17 protons in its nucleus. 

Thorium is a radioactive element that was discovered in the 1800s. The most common isotope of thorium has a mass number of 232. What is the atomic number of thorium How many neutrons does an atom of this isotope contain ... 

The atomic weight of an element comes from the nucleus. Protons and neutrons in the nucleus each have a weight of 1 AMU. Atoms of elements have varying numbers of protons and neutrons. The total number of neutrons and protons in each atom equals the atomic weight. The atomic number of an element equals the number of protons in that element. The number of neutrons is determined by subtracting the number of protons from the atomic weight what remains is the number of neutrons. In chemistry, we are concerned more with the electrons orbiting the nucleus than the nucleus itself. We are particularly interested in the electrons in the outer shell of the atom. Chemical activity takes place between the outer-shell electrons of elements this chemical activity forms compounds. In radioactivity, the concern is with the nucleus, where radiation is emitted. Radioactivity will be discussed further in Chapter 8. 

In 1915, the Enghsh physicist Henry Moseley (1887-1915) suggested that a more fundamental property of an element than its atomic weight is the number of protons in atoms of that element, what came to be called the atomic number of an element. 

The number of protons in an atom defines what element it is. For example carbon atoms have six protons, hydrogen atoms have one, and oxygen atoms have eight. The number of protons in an atom is referred to as the atomic number of that element. The number of protons in an atom also determines the chemical behavior of the element. 

The mole (mol) is the amount of a substance that contains the same number of particles as atoms in exactly 12 grams of carbon-12. This number of particles (atoms or molecules or ions) per mole is called Avogadro s number and is numerically equal to 6.022 x 1023 particles. The mole is simply a term that represents a certain number of particles, like a dozen or a pair. That relates moles to the microscopic world, but what about the macroscopic world The mole also represents a certain mass of a chemical substance. That mass is the substance s atomic or molecular mass expressed in grams. In Chapter 5, the Basics chapter, we described the atomic mass of an element in terms of atomic mass units (amu). This was the mass associated with an individual atom. Then we described how one could calculate the mass of a compound by simply adding together the masses, in amu, of the individual elements in the compound. This is still the case, but at the macroscopic level the unit of grams is used to represent the quantity of a mole. Thus, the following relationships apply ... 

An atom is the smallest particle of an element that still has all the properties of that element. Atoms are made up of three main particles. Protons and neutrons come together in an atom s nucleus, whereas electrons orbit the nucleus. The number of protons in an atom determines what type of element it is. The structure of the periodic table comes from the fact that electron shells are filled in a specific pattern. The rows of the table are called periods and the columns are called groups. There are other ways to divide up the table, as well. 

An elemental analysis of Cytochrome c, an enzyme involved in qxidation-reduction processes, gave 0.43% Fe and 1.48% S. What is the minimum molecular weight of the enzyme What is the minimum number of iron atoms per molecule Of sulfur atoms ... 

How do you determine the oxidation number for an element In most cases, you might look up the oxidation number on a periodic table or some other reference table. Often, you can predict the oxidation number of an element by its location on the periodic table. You should remember that the electron configuration, and therefore the Lewis dot notation, for many elements may be determined by locating the element on the periodic table. If you can figure out what type of ion the atom is likely to form in order to complete its valence shell, you can figure out the likely oxidation number for the element. 

EXAMPLE I (a) The atoms of a certain element have a mass 2.026 times the mass of an equal number of atoms. What is the atomic mass of the element (b) Which element is it (c) What is the best way to make sure that we get equal numbers of atoms of two elements to compare total masses ... 

What is the difference hefween the atomic number and the mass number of an element Can atoms of fwo differenf elements have the same atomic number Could they have the same mass number Explain. 

What makes an atom of one element different from an atom of another element is that the atoms of each element have a characteristic number of protons. Indeed, the number of protons in an atom of any particular element is called that element s atomic number. Because an atom has no net electrical charge, the number of electrons it contains must equal the number of protons. All atoms of carbon, for example, have six protons and six electrons, whereas all atoms of oxygen have eight protons and eight electrons. Thus, carbon has atomic number 6, and oxygen has atomic number 8. The atomic number of each element is listed with the name and symbol of the element on the inside front cover of the text. 

What is the minimum number of atoms that could be contained in the unit cell of an element with a body-centered cubic lattice ... 

If element A below gives off an alpha particle, what is the atomic number and mass of the resulting element B J°A... 

What is the difference between the mass number and the atomic mass of an element ... 

If all atoms are composed of the same subatomic particles, what makes the atoms of one element different from those of another The answer is the number of these particles. The most important number to the identity of an atom is the number of protons in its nucleus. The number of protons defines the element. For example, an atom with 2 protons in its nucleus is a helium atom, an atom with 6 protons in its nucleus is a carbon atom (Figure 2.8 ), and an atom with 92 protons in its nucleus is a uranium atom. The number of protons in an atom s nucleus is its atomic number and is given the symbol Z. The atomic numbers of known elements range from 1 to 116 (although additional elements may still be discovered), as shown in the periodic table of the elements (Figure 2.9 ). In the periodic table, described in more detail in Section 2.7, the elements are arranged so that those with similar properties are in the same column. 

Each element has a symbol.There s a particular way of writing what s in a molecule, called a chemical formula.The chemical formula lists all the elements that form each molecule and uses a small number to the bottom right of an element s symbol to stand for the number of atoms of that element. For example, the chemical formula for water is H20.That tells us that a water molecule is made up of two hydrogen ( H and 2 )... 

As you might expect, the isotopes do differ in mass. Isotopes containing more neutrons have a greater mass. In spite of differences in mass and the number of neutrons, isotopes of an atom have essentially the same chemical behavior. Why Because, as you ll learn in greater detail later in this textbook, chemical behavior is determined by the number of electrons an atom has, not by its number of neutrons and protons. To make it easy to identify each of the various isotopes of an element, chemists add a number after the element s name. The number that is added is called the mass number, and it represents the sum of the number of protons and neutrons in the nucleus. For example, the potassium isotope with 19 protons and 20 neutrons has a mass number of 39 (19 + 20 = 39), and the isotope is called potassium-39. The potassium isotope with 19 protons and 21 neutrons has a mass number of 40 (19 -I- 21 = 40), and is called potassium-40. What is the mass number and name of the potassium isotope with 19 protons and 22 neutrons ... 

C. 94 Pu + X - 94 Pu—This equation shows X on the left side of the arrow. On the right side of the arrow, we have a mass number of 240. The total of the mass numbers on the left side must also add up to 240, making the mass number of X1 (240 - 239 = 1). The atomic number of X must be 0, because we already have 94 on both sides of the equation. Can you figure out what g X represents You will not find an element with an atomic number of zero on the periodic table, so this is one of the times where it is better to think of the atomic number as the nuclear charge. 

Tip-off You are asked to determine the oxidation number of an atom, or you need to assign oxidation numbers to atoms to determine whether a reaction is a redox reaction, and if it is, to identify which element is oxidized, which is reduced, what the oxidizing agent is, and what the reducing agent is. 

What is then responsible for the periodic behavior of the elements And why do elements within a particular group have similar chemical behavior The explanation stems from the fact that atoms are attracted to each other by electric forces. The atomic number, i.e., the number of positively charged protons in the nucleus, determines how many negatively charged electrons are contained in the atoms of a particular element, and it is the outer-shell electrons, also called valence electrons, that determine the reactivity, or how strongly and in what way the atoms will bind with other atoms. The chemical behavior of an element is thus ultimately determined by the way in which the electrons orbiting its nucleus are structured. ... 

What do we mean by the average atomic mass of an element What is "averaged" to arrive at this number ... 

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