Skip to main content. Atoms, Molecules, and Ions. Search for:. The Periodic Table The Periodic Table The periodic table shows all the elements and their physical properties; it is arranged based on atomic numbers and electron configurations.
Learning Objectives Identify the common periodic trends that can be deduced from the periodic table of elements. Key Takeaways Key Points The periodic table lists all the elements, with information about their atomic weights, chemical symbols, and atomic numbers. The arrangement of the periodic table leads us to visualize certain trends among the atoms. The vertical columns groups of the periodic table are arranged such that all its elements have the same number of valence electrons.
All elements within a certain group thus share similar properties. Key Terms atomic number : The number, equal to the number of protons in an atom, that determines its chemical properties. Molecules Molecules are electrically neutral compounds made of multiple atoms bound together by chemical bonds.
Learning Objectives Recognize the general properties of molecules. Key Takeaways Key Points Molecules are neutral and do not carry any charge. A molecule may consist of nonmetallic atoms of a single chemical element, as with oxygen O 2 , or of different elements, as with water H 2 O.
The geometry and composition of a molecule will determine its chemical and physical properties. Key Terms covalent : when 2 or more nonmetallic atoms are bound together by sharing electrons. All compounds are molecules but not all molecules are compounds. Ions An ion is an atom or molecule that has a net electrical charge because its total number of electrons is not equal to its number of protons. Learning Objectives Compare the different classes of ions. Key Takeaways Key Points Ions are formed when the number of protons in an atom does not equal the number of electrons.
If more protons are present, the ion is positive and is known as a cation; if more electrons are present, the ion is negative and referred to as an anion. Key Terms ion : An atom or group of atoms bearing an electrical charge, such as the sodium and chlorine atoms in a salt solution. Unlike elements in a family, elements in a period are not alike in properties.
There are 7 periods of elements. The 2 rows that have been separated out of the main table are rare-earth elements, or lanthanons lanthanides in the first period and actinons actinides in the next period. Launch it Play obstacle! The journey towards the creation of the periodic table can be traced as far back as the Ancient Greeks of BC who used the words "element" and "atom" to describe the differences between things. The periodic table we know today was created by 4 separate European scientists during the s.
In , 44 year-old French geologist A. Meanwhile, in England, chemist John A. By , experimental evidence indicated the existence of a second particle. A proton has the same amount of charge as an electron, but its charge is positive, not negative. Another major difference between a proton and an electron is mass. Although still incredibly small, the mass of a proton is 1.
Finally, additional experiments pointed to the existence of a third particle, called the neutron. Evidence produced in established the existence of the neutron, a particle with about the same mass as a proton but with no electrical charge.
We understand now that all atoms can be broken down into subatomic particles: protons, neutrons, and electrons. Experiment have shown that protons and neutrons are concentrated in a central region of each atom called the nucleus plural, nuclei.
Electrons are outside the nucleus and orbit about it because they are attracted to the positive charge in the nucleus. As a result, an atom consists largely of empty space. Fig 2. The protons and neutrons of an atom are found clustered at the center of the atom in a structure called the nucleus. Note that most of the area of an atom is taken up by the empty space of the electron cloud. Electrons are not in discrete orbits like planets around the sun.
In both diagrams, the nucleus is in the center of the diagram. As it turns out, the number of protons that an atom holds in its nucleus is the key determining feature for its chemical properties. In short, an element is defined by the number of protons found in its nucleus.
The proton number within an element is also called its Atomic Number and is represented by the mathematical term, Z Fig 2. If you refer back to the Periodic Table of Elements shown in figure 2. Thus, as you read across each row of the Periodic Table left to right , each element increases by one proton or one Atomic Number, Z. Each element on the periodic table is represented by the atomic symbol Cu for Copper , the Atomic Number in the upper lefthand corner, and the Atomic Mass in the righthand corner.
How many neutrons are in atoms of a particular element? At first it was thought that the number of neutrons in a nucleus was also characteristic of an element. However, it was found that atoms of the same element can have different numbers of neutrons.
Atoms of the same element that have different numbers of neutrons are called isotopes Fig. Isotope composition has proven to be a useful method for dating many rock layers and fossils.
All hydrogen atoms have one proton and one electron. However, they can differ in the number of neutrons. Note that Tritium is unstable isotope and will breakdown over time. Thus, Tritium is a radioactive element. Most elements exist as mixtures of isotopes. In fact, there are currently over 3, isotopes known for all the elements. When scientists discuss individual isotopes, they need an efficient way to specify the number of neutrons in any particular nucleus.
The atomic mass A of an atom is the sum of the numbers of protons and neutrons in the nucleus Fig. Given the atomic mass for a nucleus and knowing the atomic number, Z , of that particular atom , you can determine the number of neutrons by subtracting the atomic number from the atomic mass.
Thus, we might see. The 29 is the atomic number, Z , which is the same for all copper atoms , while the 63 is the atomic mass A of the isotope. Allotropes of an element are different and separate from the term isotope and should not be confused. Some chemical elements can form more than one type of structural lattice, these different structural lattices are known as allotropes. This is the case for phosphorus as shown in Figure 2. White or yellow phosphorus forms when four phosphorus atoms align in a tetrahedral conformation Fig 2.
The other crystal lattices of phosphorus are more complex and can be formed by exposing phosphorus to different temperatures and pressures. For example, the cage-like lattice of red phosphorus can be formed by heating white phosphorus over o C Fig 2. Note that allotropic changes affect how the atoms of the element interact with one another to form a 3-dimensional structure.
They do not alter the sample with regard to the atomic isotope forms that are present, and DO NOT alter or affect the atomic mass A of the element. Different allotropes of different elements can have different physical and chemical properties and are thus, still important to consider. Atoms, Molecules, and Ions. Search for:. The Periodic Table. Learning Objective Identify the common periodic trends that can be deduced from the periodic table of elements. Key Points The periodic table lists all the elements, with information about their atomic weights, chemical symbols, and atomic numbers.
The arrangement of the periodic table leads us to visualize certain trends among the atoms. The vertical columns groups of the periodic table are arranged such that all its elements have the same number of valence electrons.
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