Atomic Structure and Periodic table

• Early attempts to arrange the elements into a periodic table were made by Johan Dober, who noted that elements with similar chemical properties often occurred in threes, and called these Triads.
• Dimitri Mendeleev developed the first modern periodic table by arranging all the elements in order of increasing atomic weight, and then switching the order of specific elements to fit the patterns of other elements in the same group.
• Dimitri Mendeleev predicted the properties of the Undiscovered elements based on other elements in the same groups.
• The modern periodic table is arranged into columns which we call groups, including group one, group two, the transition elements, groups three, four, five, six, seven, and group zero, which includes the noble gases.
• The term 'periodic' in the periodic table refers to elements with similar properties occurring at regular intervals.
• All the elements in a group in the periodic table have similar chemical properties because they have the same number of electrons in their outer energy level.
• Scientists began to wonder if the elements could be arranged into some sort of logical order around 40 years before Dimitri Mendeleev developed his periodic table.
• John Newlands arranged the elements in order of increasing atomic weight and saw that every eighth element reacts in a similar way, a pattern he called his law of octaves.
• Dimitri Mendeleev's law of octaves states that every eighth element reacts in a similar way if the elements are arranged in order of increasing atomic weight.
• Dimitri Mendeleev's periodic table was so accurate that he predicted the properties of the Undiscovered elements based on other elements in the same groups.
• The modern periodic table is almost identical to Dimitri Mendeleev's periodic table, with the exception of a few important differences.
• In the modern periodic table, the elements are arranged in order of atomic number, not atomic weight, ensuring that every element is in the correct group.
• The modern periodic table includes group zero, which includes the noble gases, elements that were not fully discovered when Dimitri Mendeleev published his table.
• Group seven elements react with metals because the group's electron gains an electron to achieve a full outer energy level.
• Fluorine is the most reactive element in group seven because the negative electron is attracted to the positive charge of the nucleus.
• As we move down group seven, the elements become less reactive due to increased distance and increased shielding.
• More reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
• The reaction between the compound sodium bromide and the element fluorine is an example of a displacement reaction, where fluorine, being more reactive, can push out or displace bromine.
• In a displacement reaction, the element that is displaced is referred to as the displaced element.
• Chlorine is more reactive than iodine because it has a greater distance between the outer energy level and the nucleus and its outer energy level is shielded from the positive charge of the nucleus by internal electrons.
• In a displacement reaction, the element that is displaced cannot displace the other element, resulting in no reaction.
• Group seven elements, also known as the halogens, form covalent compounds when they react with nonmetals.
• Group seven elements form ionic compounds when they react with metals.
• Group seven elements, also known as the halogens, are all nonmetals.
• Group seven elements have seven electrons in the outer energy level.
• Group seven elements form molecules with two atoms joined by a single covalent bond.
• Group seven elements form covalent compounds when they react with other nonmetal atoms.
• All of the elements in group seven form covalent compounds when they react with other nonmetal elements.
• Halogens form covalent compounds with other nonmetals.
• When Group seven elements react with metals, they form ionic compounds.
• Chlorine, a Group seven element, reacts with the metal lithium, which has one electron in its outer energy level, forming the ionic compound LiCl.
• Chlorine, with 17 protons and 18 electrons, has an overall -1 charge, which is represented by the chloride ion Cl-.
• When any group of an element reacts to the metal, the group 7 element gains one electron and forms a 1- ion.
• Group 7 ions, including fluoride and chloride, end in ID instead of -ide.
• Group seven elements, also known as the halogens, have seven electrons in their two energy levels.
• When two atoms of a group seven element react, they form a covalent bond.
• Group seven elements form molecules consisting of two atoms joined by a covalent bond.
• The melting and boiling point of the group seven elements increases as we move down the group.
• Fluorine and chlorine are both gases at room temperature because their boiling points are lower than 20 degrees Celsius.
• Bromine is a liquid at room temperature because its melting point is lower than 20 degrees Celsius.