In one sentence, describe what the following article is about: Most elements can naturally occur in multiple forms, or isotopes. The mass number for each isotope is the sum of numbers of protons and neutrons in the nucleus. Each proton and each neutron weigh 1 atomic mass unit (amu). The only difference between two isotopes of the same element is the number of neutrons per atom, which affects the atom's mass. However, the element always has the same number of protons.  The average atomic mass of the element takes the variations of the number of neutrons into account, and tells you the average mass per atom in a typical sample of that element. For example, the element silver (Ag) has two naturally occurring isotopes: Ag-107 and Ag-109 (or 107Ag and 109Ag). Isotopes are named after the "mass number," or the sum of protons and neutrons in one atom. This means Ag-109 has two more neutrons per atom than Ag-107, giving it slightly more mass. You'll need two pieces of information for each isotope, which you can look up in a reference book or an online source such as webelements.com. The first is the atomic mass, or the mass of one atom of each isotope. Isotopes with more neutrons have more mass.  For example, the silver isotope Ag-107 has an atomic mass of 106.90509 amu (atomic mass units). The isotope Ag-109 is slightly heavier with a mass of 108.90470. The last couple decimal places might be slightly different in different sources. Don't include any numbers in parentheses after the mass. The abundance tells you how common the isotope is, as a percentage of all atoms of the element. Each isotope contributes proportionally to its abundance (the more abundant the isotope, the more it will contribute to the average atomic mass). You can find this in the same source you found the mass. The abundances of all isotopes should add up to 100% (though it might be slightly off due to rounding errors).  The isotope Ag-107 has an abundance of 51.86%. Ag-109 is slightly less common with an abundance of 48.14%. This means that a typical sample of silver is 51.86% Ag-107 and 48.14% Ag-109. Ignore any isotopes that do not have an abundance listed. These isotopes do not occur naturally on Earth. Divide the abundance percentage by 100 to get the same value as a decimal. In the sample problem, the abundance figures are 51.86 / 100 = 0.5186 and 48.14 / 100 = 0.4814. The average atomic mass of an element with n isotopes equals (massisotope 1 * abundanceisotope 1) + (massisotope 2 * abundanceisotope 2) + ... + (massisotope n * abundanceisotope n. This is an example of a "weighted average," meaning that more common (more abundant) masses have a greater effect on the result. Here's how to use this formula for silver:  Average atomic massAg = (massAg-107 * abundanceAg-107) + (massAg-109 * abundanceAg-109)=(106.90509 * 0.5186) + (108.90470 * 0.4814)= 55.4410 + 52.4267= 107.8677 amu. Look up the element on a periodic table to check your answer. The average atomic mass is usually written underneath the element symbol.
Summary: Understand isotopes and atomic masses. Look up the mass of each isotope. Write down the abundance of each isotope. Turn your abundance percentages into decimals. Find the weighted average of the atomic mass of its stable isotopes.

In one sentence, describe what the following article is about: Go to https://www.facebook.com in your browser. This will open your News Feed if you're logged into Facebook. If you aren't logged into Facebook, enter your email address (or phone number) in the top right corner of the screen and click Log In. It's the globe-shaped icon in the top-right side of the page. Doing so will open a drop-down menu containing your recent Facebook notifications. Place your mouse's pointer over a notification that you want to delete. Doing so will cause a ⋯ icon and a circle to appear on the right side of the notification.  For example, if you want to remove a notification about a friend liking your status, you'd place the mouse cursor over "[Name] likes your post: [Post]." If you don't see the notification that you want to delete, click See All at the bottom of the drop-down menu, then scroll down until you find the notification. This button is on the far-right side of the notification's box. Clicking it prompts a pop-up menu to appear. It's in the pop-up menu. Doing so will remove the notification from the "Notifications" menu.
Summary: Open Facebook. Click the "Notifications" icon. Select a notification. Click ⋯. Click Hide this notification.

In one sentence, describe what the following article is about: Remove the skewers from the grill with a pair of tongs and pile them on a separate clean plate. There will be a lot of heat trapped in between the layers, so wait a few minutes before you dig in. By the time you finish getting the rest of the meal together, the sprouts should have cooled down enough to eat. You can either leave the sprouts on the skewers to keep things simple, or scrape them off into a larger serving bowl that you can pass around the table. Flame-fired brussels sprouts pair perfectly with hearty grill staples like steaks, chicken, chops, or salmon. They'll also be right at home among the usual lineup of summer veggies, including corn on the cob and sliced tomatoes. They're such a versatile ingredient that you can't go wrong! Make your grilled brussels sprouts a featured dish in a vegan or vegetarian meal.
Summary:
Allow the sprouts to cool before eating. Serve with your favorite grilled foods.